

<!--XBRL Document Created with Wdesk from Workiva, formerly WebFilings-->
<!-- -->
<linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <roleRef roleURI="http://www.rubiconproject.com/role/A401KSavingsPlan" xlink:href="rubi-20141231.xsd#A401KSavingsPlan" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/A401KSavingsPlanDetails" xlink:href="rubi-20141231.xsd#A401KSavingsPlanDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpenses" xlink:href="rubi-20141231.xsd#AccountsPayableAndAccruedExpenses" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpensesDetails" xlink:href="rubi-20141231.xsd#AccountsPayableAndAccruedExpensesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpensesNarrativeDetails" xlink:href="rubi-20141231.xsd#AccountsPayableAndAccruedExpensesNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpensesTables" xlink:href="rubi-20141231.xsd#AccountsPayableAndAccruedExpensesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies" xlink:href="rubi-20141231.xsd#BasisOfPresentationAndSummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesIntangibleAssetsDetails" xlink:href="rubi-20141231.xsd#BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesIntangibleAssetsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:href="rubi-20141231.xsd#BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:href="rubi-20141231.xsd#BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentNetDetails" xlink:href="rubi-20141231.xsd#BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentNetDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTables" xlink:href="rubi-20141231.xsd#BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BusinessCombinations" xlink:href="rubi-20141231.xsd#BusinessCombinations" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BusinessCombinationsAcquiredIntangibleAssetsAndEstimatedUsefulLivesDetails" xlink:href="rubi-20141231.xsd#BusinessCombinationsAcquiredIntangibleAssetsAndEstimatedUsefulLivesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BusinessCombinationsAllocationOfTotalPurchaseConsiderationsDetails" xlink:href="rubi-20141231.xsd#BusinessCombinationsAllocationOfTotalPurchaseConsiderationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BusinessCombinationsNarrativeDetails" xlink:href="rubi-20141231.xsd#BusinessCombinationsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BusinessCombinationsProFormaInformationDetails" xlink:href="rubi-20141231.xsd#BusinessCombinationsProFormaInformationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/BusinessCombinationsTables" xlink:href="rubi-20141231.xsd#BusinessCombinationsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/Capitalization" xlink:href="rubi-20141231.xsd#Capitalization" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CapitalizationConvertiblePreferredStockDetails" xlink:href="rubi-20141231.xsd#CapitalizationConvertiblePreferredStockDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CapitalizationNarrativeDetails" xlink:href="rubi-20141231.xsd#CapitalizationNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CapitalizationTables" xlink:href="rubi-20141231.xsd#CapitalizationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CommitmentsAndContingencies" xlink:href="rubi-20141231.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CommitmentsAndContingenciesDetails" xlink:href="rubi-20141231.xsd#CommitmentsAndContingenciesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CommitmentsAndContingenciesOperatingLeasesFutureMinimumPaymentsDueDetails" xlink:href="rubi-20141231.xsd#CommitmentsAndContingenciesOperatingLeasesFutureMinimumPaymentsDueDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CommitmentsAndContingenciesOtherContractsDetails" xlink:href="rubi-20141231.xsd#CommitmentsAndContingenciesOtherContractsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/CommitmentsAndContingenciesTables" xlink:href="rubi-20141231.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/ConsolidatedBalanceSheets" xlink:href="rubi-20141231.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="rubi-20141231.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/ConsolidatedStatementOfCashFlows" xlink:href="rubi-20141231.xsd#ConsolidatedStatementOfCashFlows" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/ConsolidatedStatementOfComprehensiveLoss" xlink:href="rubi-20141231.xsd#ConsolidatedStatementOfComprehensiveLoss" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/ConsolidatedStatementOfConvertiblePreferredStockAndStockholdersEquityDeficit" xlink:href="rubi-20141231.xsd#ConsolidatedStatementOfConvertiblePreferredStockAndStockholdersEquityDeficit" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/ConsolidatedStatementOfOperations" xlink:href="rubi-20141231.xsd#ConsolidatedStatementOfOperations" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangements" xlink:href="rubi-20141231.xsd#DebtAndCapitalLeaseArrangements" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangementsDebtAndCapitalLeaseArrangementsDetails" xlink:href="rubi-20141231.xsd#DebtAndCapitalLeaseArrangementsDebtAndCapitalLeaseArrangementsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangementsNarrativeDetails" xlink:href="rubi-20141231.xsd#DebtAndCapitalLeaseArrangementsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangementsTables" xlink:href="rubi-20141231.xsd#DebtAndCapitalLeaseArrangementsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/DocumentAndEntityInformation" xlink:href="rubi-20141231.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/FairValueMeasurements" xlink:href="rubi-20141231.xsd#FairValueMeasurements" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/FairValueMeasurementsChangeInFairValueDetails" xlink:href="rubi-20141231.xsd#FairValueMeasurementsChangeInFairValueDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/FairValueMeasurementsFinancialInstrumentsDetails" xlink:href="rubi-20141231.xsd#FairValueMeasurementsFinancialInstrumentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/FairValueMeasurementsNarrativeDetails" xlink:href="rubi-20141231.xsd#FairValueMeasurementsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/FairValueMeasurementsTables" xlink:href="rubi-20141231.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/FairValueMeasurementsWeightedAverageAssumptionsDetails" xlink:href="rubi-20141231.xsd#FairValueMeasurementsWeightedAverageAssumptionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GeographicInformation" xlink:href="rubi-20141231.xsd#GeographicInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GeographicInformationDetails" xlink:href="rubi-20141231.xsd#GeographicInformationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GeographicInformationTables" xlink:href="rubi-20141231.xsd#GeographicInformationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssets" xlink:href="rubi-20141231.xsd#GoodwillAndIntangibleAssets" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsFiniteLivedIntangibleAssetsDetails" xlink:href="rubi-20141231.xsd#GoodwillAndIntangibleAssetsFiniteLivedIntangibleAssetsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsFiniteLivedIntangibleAssetsFutureAmortizationExpenseDetails" xlink:href="rubi-20141231.xsd#GoodwillAndIntangibleAssetsFiniteLivedIntangibleAssetsFutureAmortizationExpenseDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsGoodwillDetails" xlink:href="rubi-20141231.xsd#GoodwillAndIntangibleAssetsGoodwillDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsNarrativeDetails" xlink:href="rubi-20141231.xsd#GoodwillAndIntangibleAssetsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsTables" xlink:href="rubi-20141231.xsd#GoodwillAndIntangibleAssetsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxes" xlink:href="rubi-20141231.xsd#IncomeTaxes" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails" xlink:href="rubi-20141231.xsd#IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:href="rubi-20141231.xsd#IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails" xlink:href="rubi-20141231.xsd#IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesIncomeBeforeIncomeTaxDomesticAndForeignDetails" xlink:href="rubi-20141231.xsd#IncomeTaxesIncomeBeforeIncomeTaxDomesticAndForeignDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesNarrativeDetails" xlink:href="rubi-20141231.xsd#IncomeTaxesNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesTables" xlink:href="rubi-20141231.xsd#IncomeTaxesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/IncomeTaxesUnrecognizedTaxBenefitsDetails" xlink:href="rubi-20141231.xsd#IncomeTaxesUnrecognizedTaxBenefitsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCosts" xlink:href="rubi-20141231.xsd#InternalUseSoftwareDevelopmentCosts" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCostsDetails" xlink:href="rubi-20141231.xsd#InternalUseSoftwareDevelopmentCostsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCostsNarrativeDetails" xlink:href="rubi-20141231.xsd#InternalUseSoftwareDevelopmentCostsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCostsTables" xlink:href="rubi-20141231.xsd#InternalUseSoftwareDevelopmentCostsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NatureOfOperations" xlink:href="rubi-20141231.xsd#NatureOfOperations" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NatureOfOperationsDetails" xlink:href="rubi-20141231.xsd#NatureOfOperationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholders" xlink:href="rubi-20141231.xsd#NetLossPerShareAttributableToCommonStockholders" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersAntiDilutiveDetails" xlink:href="rubi-20141231.xsd#NetLossPerShareAttributableToCommonStockholdersAntiDilutiveDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersDetails" xlink:href="rubi-20141231.xsd#NetLossPerShareAttributableToCommonStockholdersDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersNarrativeDetails" xlink:href="rubi-20141231.xsd#NetLossPerShareAttributableToCommonStockholdersNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersTables" xlink:href="rubi-20141231.xsd#NetLossPerShareAttributableToCommonStockholdersTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/PropertyAndEquipment" xlink:href="rubi-20141231.xsd#PropertyAndEquipment" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/PropertyAndEquipmentDetails" xlink:href="rubi-20141231.xsd#PropertyAndEquipmentDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/PropertyAndEquipmentNarrativeDetails" xlink:href="rubi-20141231.xsd#PropertyAndEquipmentNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/PropertyAndEquipmentTables" xlink:href="rubi-20141231.xsd#PropertyAndEquipmentTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/RelatedPartyTransactions" xlink:href="rubi-20141231.xsd#RelatedPartyTransactions" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/RelatedPartyTransactionsDetails" xlink:href="rubi-20141231.xsd#RelatedPartyTransactionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensation" xlink:href="rubi-20141231.xsd#StockBasedCompensation" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationEmployeeStockPurchasePlanDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationEmployeeStockPurchasePlanDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationExpenseDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationExpenseDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockActivityDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationRestrictedStockActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockNarrativeDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationRestrictedStockNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockUnitsActivityDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationRestrictedStockUnitsActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockUnitsNarrativeDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationRestrictedStockUnitsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationStockOptionsNarrativeDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationStockOptionsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationStockOptionsOutstandingDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationStockOptionsOutstandingDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationTables" xlink:href="rubi-20141231.xsd#StockBasedCompensationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/StockBasedCompensationValuationAssumptionsDetails" xlink:href="rubi-20141231.xsd#StockBasedCompensationValuationAssumptionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/SubsequentEvents" xlink:href="rubi-20141231.xsd#SubsequentEvents" xlink:type="simple" />
  <roleRef roleURI="http://www.rubiconproject.com/role/SubsequentEventsDetails" xlink:href="rubi-20141231.xsd#SubsequentEventsDetails" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/A401KSavingsPlan" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/A401KSavingsPlanDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpenses" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpensesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpensesNarrativeDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/AccountsPayableAndAccruedExpensesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesIntangibleAssetsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0BDF7E9E18889E176DE7BA2AF340739D" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_B6035A178B7AE8A92651BA2AF33E6B44" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0BDF7E9E18889E176DE7BA2AF340739D" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_B6035A178B7AE8A92651BA2AF33E6B44" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DD61B1E44C71A8B5F031BA2AF33E21F9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_B6035A178B7AE8A92651BA2AF33E6B44" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DD61B1E44C71A8B5F031BA2AF33E21F9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DD61B1E44C71A8B5F031BA2AF33E21F9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DD61B1E44C71A8B5F031BA2AF33E21F9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_D95E1E6789C703FFEBF1BA2AF33FB7D8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_D95E1E6789C703FFEBF1BA2AF33FB7D8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_7103866C8C1E87D7C457BA2AF33F458D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_7103866C8C1E87D7C457BA2AF33F458D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaap_CustomerRelationshipsMember_CD20CE38F357BCF9B7C1BA2AF33F6629" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600" xlink:to="loc_us-gaap_CustomerRelationshipsMember_CD20CE38F357BCF9B7C1BA2AF33F6629" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_823C1A5C3E56076A3FDDBA2AF33FF6D5" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5581C6DE1B17331F2AF9BA2AF33FA600" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_823C1A5C3E56076A3FDDBA2AF33FF6D5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_E8BB6A253ADAEA76D8B1BA2AF33F86BE" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_B6035A178B7AE8A92651BA2AF33E6B44" xlink:to="loc_us-gaap_RangeAxis_E8BB6A253ADAEA76D8B1BA2AF33F86BE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_8DBC4E9E57C6C799D2C0BA2AF33F32CC_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_E8BB6A253ADAEA76D8B1BA2AF33F86BE" xlink:to="loc_us-gaap_RangeMember_8DBC4E9E57C6C799D2C0BA2AF33F32CC_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_8DBC4E9E57C6C799D2C0BA2AF33F32CC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_E8BB6A253ADAEA76D8B1BA2AF33F86BE" xlink:to="loc_us-gaap_RangeMember_8DBC4E9E57C6C799D2C0BA2AF33F32CC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_092D2F2B03B25DD9FE69BA2AF33F1C73" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_8DBC4E9E57C6C799D2C0BA2AF33F32CC" xlink:to="loc_us-gaap_MinimumMember_092D2F2B03B25DD9FE69BA2AF33F1C73" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_8A12F7219BCD8584B4EDBA2AF3402851" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_8DBC4E9E57C6C799D2C0BA2AF33F32CC" xlink:to="loc_us-gaap_MaximumMember_8A12F7219BCD8584B4EDBA2AF3402851" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_6BA7265ED27B2F75FF15BA2AF34018AC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0BDF7E9E18889E176DE7BA2AF340739D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_6BA7265ED27B2F75FF15BA2AF34018AC" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_A6471202CDDA3283CB78D77229258BB3" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:label="loc_us-gaap_ConcentrationRiskTable_B42711C7833A95ABF5D0D77229247F37" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_A6471202CDDA3283CB78D77229258BB3" xlink:to="loc_us-gaap_ConcentrationRiskTable_B42711C7833A95ABF5D0D77229247F37" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_37D0D56E85B856C4641BD7722924C703" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_B42711C7833A95ABF5D0D77229247F37" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_37D0D56E85B856C4641BD7722924C703" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_E662B1D6DA036F81F088D7722924A960_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_37D0D56E85B856C4641BD7722924C703" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_E662B1D6DA036F81F088D7722924A960_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_E662B1D6DA036F81F088D7722924A960" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_37D0D56E85B856C4641BD7722924C703" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_E662B1D6DA036F81F088D7722924A960" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CreditConcentrationRiskMember" xlink:label="loc_us-gaap_CreditConcentrationRiskMember_38715F51C3C304C3D7CFD7722924F913" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_E662B1D6DA036F81F088D7722924A960" xlink:to="loc_us-gaap_CreditConcentrationRiskMember_38715F51C3C304C3D7CFD7722924F913" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SupplierConcentrationRiskMember" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_87F3EFE29900B1F3666BD7722924C644" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_E662B1D6DA036F81F088D7722924A960" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_87F3EFE29900B1F3666BD7722924C644" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_DC5F2990C8359A7606C4D77229248251" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_B42711C7833A95ABF5D0D77229247F37" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_DC5F2990C8359A7606C4D77229248251" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_DF5DB5B507BE45CE87FED77229256317_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_DC5F2990C8359A7606C4D77229248251" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_DF5DB5B507BE45CE87FED77229256317_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_DF5DB5B507BE45CE87FED77229256317" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_DC5F2990C8359A7606C4D77229248251" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_DF5DB5B507BE45CE87FED77229256317" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccountsReceivableMember" xlink:label="loc_us-gaap_AccountsReceivableMember_DFE2309F2D41D2447EC2D7722925E84E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_DF5DB5B507BE45CE87FED77229256317" xlink:to="loc_us-gaap_AccountsReceivableMember_DFE2309F2D41D2447EC2D7722925E84E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccountsPayableMember" xlink:label="loc_us-gaap_AccountsPayableMember_A233094B12E4F772D032D77229251967" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_DF5DB5B507BE45CE87FED77229256317" xlink:to="loc_us-gaap_AccountsPayableMember_A233094B12E4F772D032D77229251967" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MajorCustomersAxis" xlink:label="loc_us-gaap_MajorCustomersAxis_EEE379FA68F80B01A125D77229250372" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_B42711C7833A95ABF5D0D77229247F37" xlink:to="loc_us-gaap_MajorCustomersAxis_EEE379FA68F80B01A125D77229250372" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_E8D24DF763B03D23E83BD772292591A7_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorCustomersAxis_EEE379FA68F80B01A125D77229250372" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_E8D24DF763B03D23E83BD772292591A7_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_E8D24DF763B03D23E83BD772292591A7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorCustomersAxis_EEE379FA68F80B01A125D77229250372" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_E8D24DF763B03D23E83BD772292591A7" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_CustomerOneMember" xlink:label="loc_rubi_CustomerOneMember_962FFE580F5D7A73755DD772292533A2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_E8D24DF763B03D23E83BD772292591A7" xlink:to="loc_rubi_CustomerOneMember_962FFE580F5D7A73755DD772292533A2" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_CustomerTwoMember" xlink:label="loc_rubi_CustomerTwoMember_DF832797B6830E9BEBF6D7722925CE5F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_E8D24DF763B03D23E83BD772292591A7" xlink:to="loc_rubi_CustomerTwoMember_DF832797B6830E9BEBF6D7722925CE5F" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ConcentrationRiskNumberOfBuyers" xlink:label="loc_rubi_ConcentrationRiskNumberOfBuyers_CF3FC43778A9184752A5D77229253D56" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_A6471202CDDA3283CB78D77229258BB3" xlink:to="loc_rubi_ConcentrationRiskNumberOfBuyers_CF3FC43778A9184752A5D77229253D56" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_83FBF0B3783EDC65A1DED77229259ACD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_A6471202CDDA3283CB78D77229258BB3" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_83FBF0B3783EDC65A1DED77229259ACD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_88F938C5B54A83876405D772292698D1" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_0EB1DBDBC7261871B910D7722925F7C5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_88F938C5B54A83876405D772292698D1" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_0EB1DBDBC7261871B910D7722925F7C5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_1C0570B517284EDA091FD7722925E047" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_0EB1DBDBC7261871B910D7722925F7C5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_1C0570B517284EDA091FD7722925E047" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_8C669072AAD5DB75BAF8D7722925245D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1C0570B517284EDA091FD7722925E047" xlink:to="loc_us-gaap_ClassOfStockDomain_8C669072AAD5DB75BAF8D7722925245D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_8C669072AAD5DB75BAF8D7722925245D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1C0570B517284EDA091FD7722925E047" xlink:to="loc_us-gaap_ClassOfStockDomain_8C669072AAD5DB75BAF8D7722925245D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_7BA59EA9836D9997AA9BD77229252ACD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8C669072AAD5DB75BAF8D7722925245D" xlink:to="loc_us-gaap_CommonClassAMember_7BA59EA9836D9997AA9BD77229252ACD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_8B431193AC9B2019D60CD77229261CC6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_0EB1DBDBC7261871B910D7722925F7C5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_8B431193AC9B2019D60CD77229261CC6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_A56F83CD6D3DC5071A43D772292647C0_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8B431193AC9B2019D60CD77229261CC6" xlink:to="loc_us-gaap_EquityComponentDomain_A56F83CD6D3DC5071A43D772292647C0_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_A56F83CD6D3DC5071A43D772292647C0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8B431193AC9B2019D60CD77229261CC6" xlink:to="loc_us-gaap_EquityComponentDomain_A56F83CD6D3DC5071A43D772292647C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_ADD5199A71AEC10D6853D77229261AE5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_A56F83CD6D3DC5071A43D772292647C0" xlink:to="loc_us-gaap_CommonStockMember_ADD5199A71AEC10D6853D77229261AE5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_EF2E6A14394385C18B1FD7722926F659" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_88F938C5B54A83876405D772292698D1" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_EF2E6A14394385C18B1FD7722926F659" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_50691435AA0C376244BBD79DB7BBE35B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_88F938C5B54A83876405D772292698D1" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_50691435AA0C376244BBD79DB7BBE35B" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentNetDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DD3A5CBBBF7D5564FBBE99D8E3B2CD0A" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_CE37060F3B15B6AB078D99D8E3B1C7E6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DD3A5CBBBF7D5564FBBE99D8E3B2CD0A" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_CE37060F3B15B6AB078D99D8E3B1C7E6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0599184D48D1CD2FEAD799D8E3B1E16F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_CE37060F3B15B6AB078D99D8E3B1C7E6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0599184D48D1CD2FEAD799D8E3B1E16F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0599184D48D1CD2FEAD799D8E3B1E16F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_0599184D48D1CD2FEAD799D8E3B1E16F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_B82C6B62A7DE0460341B99D8E3B197CE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_B82C6B62A7DE0460341B99D8E3B197CE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaap_ComputerEquipmentMember_8ED6B504374781D91DB799D8E3B1AB22" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A" xlink:to="loc_us-gaap_ComputerEquipmentMember_8ED6B504374781D91DB799D8E3B1AB22" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_6555E20DF91D19567D1299D8E3B14F40" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C3DC1B9C2385C04530C999D8E3B1047A" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_6555E20DF91D19567D1299D8E3B14F40" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_2011D3525D72C3AA948E99D8E3B14922" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_CE37060F3B15B6AB078D99D8E3B1C7E6" xlink:to="loc_us-gaap_RangeAxis_2011D3525D72C3AA948E99D8E3B14922" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_DA891DE19CC1819A7DA399D8E3B16D12_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_2011D3525D72C3AA948E99D8E3B14922" xlink:to="loc_us-gaap_RangeMember_DA891DE19CC1819A7DA399D8E3B16D12_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_DA891DE19CC1819A7DA399D8E3B16D12" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_2011D3525D72C3AA948E99D8E3B14922" xlink:to="loc_us-gaap_RangeMember_DA891DE19CC1819A7DA399D8E3B16D12" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_B1409A18DE953516FCB999D8E3B1D290" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_DA891DE19CC1819A7DA399D8E3B16D12" xlink:to="loc_us-gaap_MinimumMember_B1409A18DE953516FCB999D8E3B1D290" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_52BA0CE65245016B117D99D8E3B2EDB6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_DA891DE19CC1819A7DA399D8E3B16D12" xlink:to="loc_us-gaap_MaximumMember_52BA0CE65245016B117D99D8E3B2EDB6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_DBD11782E21CF34A7D1399D8E3B25F36" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_DD3A5CBBBF7D5564FBBE99D8E3B2CD0A" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_DBD11782E21CF34A7D1399D8E3B25F36" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BusinessCombinations" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BusinessCombinationsAcquiredIntangibleAssetsAndEstimatedUsefulLivesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_72AA77C192CB76F14950B4616A1C8EFB" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_84E7FDB9DE29CAE46AD5B4616A1BB095" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_72AA77C192CB76F14950B4616A1C8EFB" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_84E7FDB9DE29CAE46AD5B4616A1BB095" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_E6969291FC7305ACC529B4616A1BF17F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_84E7FDB9DE29CAE46AD5B4616A1BB095" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_E6969291FC7305ACC529B4616A1BF17F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_E6969291FC7305ACC529B4616A1BF17F" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_E6969291FC7305ACC529B4616A1BF17F" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ISocketIncMember" xlink:label="loc_rubi_ISocketIncMember_95EF23A1146BDDD2F78FB463EF89707E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822" xlink:to="loc_rubi_ISocketIncMember_95EF23A1146BDDD2F78FB463EF89707E" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ShinyIncMember" xlink:label="loc_rubi_ShinyIncMember_FFD1746A1BDEA38350A2B46660C6DF91" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822" xlink:to="loc_rubi_ShinyIncMember_FFD1746A1BDEA38350A2B46660C6DF91" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_MobSmithMember" xlink:label="loc_rubi_MobSmithMember_D8DB6CFF266D9EC67983B46245D5A2C1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_58063B0BF9F810EBF94DB4616A1CB822" xlink:to="loc_rubi_MobSmithMember_D8DB6CFF266D9EC67983B46245D5A2C1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3741C811325BC97B350DB4616A1C2BA5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_84E7FDB9DE29CAE46AD5B4616A1BB095" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3741C811325BC97B350DB4616A1C2BA5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3741C811325BC97B350DB4616A1C2BA5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3741C811325BC97B350DB4616A1C2BA5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_3E13C8B422101D9843C9B46245F6E6FD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_3E13C8B422101D9843C9B46245F6E6FD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaap_CustomerRelationshipsMember_E29E363B2ECA8B134B72B4624648D544" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972" xlink:to="loc_us-gaap_CustomerRelationshipsMember_E29E363B2ECA8B134B72B4624648D544" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_A8FB2D0849AAB1823123B462461CD1BD" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_A8FB2D0849AAB1823123B462461CD1BD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TrademarksMember" xlink:label="loc_us-gaap_TrademarksMember_BD13CF78DF5DAF5912D1B46246742B2B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_E51030FDD4B5B0F12CEDB4616A1C0972" xlink:to="loc_us-gaap_TrademarksMember_BD13CF78DF5DAF5912D1B46246742B2B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_08EB9F87266993A590C1B461F67181CB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_72AA77C192CB76F14950B4616A1C8EFB" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_08EB9F87266993A590C1B461F67181CB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_0BB2F2CDB656380724DDB461F683B6A0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_72AA77C192CB76F14950B4616A1C8EFB" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_0BB2F2CDB656380724DDB461F683B6A0" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BusinessCombinationsAllocationOfTotalPurchaseConsiderationsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8CA0CEE85A924A2F4333EC65AC7471ED" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8CA0CEE85A924A2F4333EC65AC7471ED" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_A25E3DA9E18FE26A0DA2EC65AC7433D7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8CA0CEE85A924A2F4333EC65AC7471ED" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_A25E3DA9E18FE26A0DA2EC65AC7433D7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_A25E3DA9E18FE26A0DA2EC65AC7433D7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_A25E3DA9E18FE26A0DA2EC65AC7433D7" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ISocketIncMember" xlink:label="loc_rubi_ISocketIncMember_4EC1947DDC12C1721FE4EC65AC74FD35" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009" xlink:to="loc_rubi_ISocketIncMember_4EC1947DDC12C1721FE4EC65AC74FD35" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ShinyIncMember" xlink:label="loc_rubi_ShinyIncMember_5CC32107022956AA3CE9EC65AC746A83" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009" xlink:to="loc_rubi_ShinyIncMember_5CC32107022956AA3CE9EC65AC746A83" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_MobSmithMember" xlink:label="loc_rubi_MobSmithMember_E20B13CB18931E85C4D4EC65AC75DF2B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_D1279F26CBF814875E53EC65AC743009" xlink:to="loc_rubi_MobSmithMember_E20B13CB18931E85C4D4EC65AC75DF2B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_268865F6155D4225F91DEC65AC75688E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_268865F6155D4225F91DEC65AC75688E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_68955A255EC72FDF76E1EC65AC75056F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_68955A255EC72FDF76E1EC65AC75056F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_095064DD1F4F55438C2BEC65AC75C1DA" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_095064DD1F4F55438C2BEC65AC75C1DA" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationConsiderationTransferredStockOptionsExchanged" xlink:label="loc_rubi_BusinessCombinationConsiderationTransferredStockOptionsExchanged_1EF84F3815E9DEA89D2FEC65AC75A502" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_rubi_BusinessCombinationConsiderationTransferredStockOptionsExchanged_1EF84F3815E9DEA89D2FEC65AC75A502" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationConsiderationTransferredandContingentConsideration" xlink:label="loc_rubi_BusinessCombinationConsiderationTransferredandContingentConsideration_5D4D07C9884DC3227DC2EC65AC75353A" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_rubi_BusinessCombinationConsiderationTransferredandContingentConsideration_5D4D07C9884DC3227DC2EC65AC75353A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_BAB5BE1F31C88DEA6E19EC65AC75C86F" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_BAB5BE1F31C88DEA6E19EC65AC75C86F" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAssetsCashandOtherAssets" xlink:label="loc_rubi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAssetsCashandOtherAssets_48644D273BAEC2726DFEEC65AC753B08" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_rubi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAssetsCashandOtherAssets_48644D273BAEC2726DFEEC65AC753B08" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_CC6B8B1E6F7BFE443419EC65AC752088" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_CC6B8B1E6F7BFE443419EC65AC752088" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_DCB2CBD6033260184B20EC65AC76E974" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_Goodwill_DCB2CBD6033260184B20EC65AC76E974" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLiabilitiesOther" xlink:label="loc_rubi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLiabilitiesOther_3A151F2AD81C1B83C759EC65AC76CD48" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_rubi_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLiabilitiesOther_3A151F2AD81C1B83C759EC65AC76CD48" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_2B9A3C9021AE680914CAEC65AC760361" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_2B9A3C9021AE680914CAEC65AC760361" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_95401C54BCB76EC08F8FEC65AC758C6F" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6C62429A5F995807D003EC65AC75D721" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_95401C54BCB76EC08F8FEC65AC758C6F" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BusinessCombinationsNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8C1674178A3091A1E004EB3A01F52544" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8C1674178A3091A1E004EB3A01F52544" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_2B9BDAED20FEDCA96428EB3A01F57D44" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8C1674178A3091A1E004EB3A01F52544" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_2B9BDAED20FEDCA96428EB3A01F57D44" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_2B9BDAED20FEDCA96428EB3A01F57D44" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_2B9BDAED20FEDCA96428EB3A01F57D44" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ISocketIncMember" xlink:label="loc_rubi_ISocketIncMember_A61EC531DA6711D21620EB3A01F6CB67" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73" xlink:to="loc_rubi_ISocketIncMember_A61EC531DA6711D21620EB3A01F6CB67" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ShinyIncMember" xlink:label="loc_rubi_ShinyIncMember_70028C5E3959AD317BCDEB3A01F67E33" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73" xlink:to="loc_rubi_ShinyIncMember_70028C5E3959AD317BCDEB3A01F67E33" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_MobSmithMember" xlink:label="loc_rubi_MobSmithMember_17D68403CD4B14E58CC6EB3A01F6FE1B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2EC17FFFB3AB910A4E7AEB3A01F6DE73" xlink:to="loc_rubi_MobSmithMember_17D68403CD4B14E58CC6EB3A01F6FE1B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_C66B1977CDB97484BF4BEB3A01F699BB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8C1674178A3091A1E004EB3A01F52544" xlink:to="loc_us-gaap_StatementClassOfStockAxis_C66B1977CDB97484BF4BEB3A01F699BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D70AC271467F785F3ED1EB3A01F6B56F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_C66B1977CDB97484BF4BEB3A01F699BB" xlink:to="loc_us-gaap_ClassOfStockDomain_D70AC271467F785F3ED1EB3A01F6B56F_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D70AC271467F785F3ED1EB3A01F6B56F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_C66B1977CDB97484BF4BEB3A01F699BB" xlink:to="loc_us-gaap_ClassOfStockDomain_D70AC271467F785F3ED1EB3A01F6B56F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_E471393CEAB86C30B71AEB3A01F62748" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_D70AC271467F785F3ED1EB3A01F6B56F" xlink:to="loc_us-gaap_CommonStockMember_E471393CEAB86C30B71AEB3A01F62748" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_250EE938D61B69ECADE6EB3A01F60F0B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_D70AC271467F785F3ED1EB3A01F6B56F" xlink:to="loc_us-gaap_CommonClassAMember_250EE938D61B69ECADE6EB3A01F60F0B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_B006638D3DC77A0DD51AEB3A01F6006C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8C1674178A3091A1E004EB3A01F52544" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_B006638D3DC77A0DD51AEB3A01F6006C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_379D41C1D7BA84D017FDEB3A01F692AF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_B006638D3DC77A0DD51AEB3A01F6006C" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_379D41C1D7BA84D017FDEB3A01F692AF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_379D41C1D7BA84D017FDEB3A01F692AF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_B006638D3DC77A0DD51AEB3A01F6006C" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_379D41C1D7BA84D017FDEB3A01F692AF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_7FC4DEB09A3D6C867E42EB3A01F6A2E3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_379D41C1D7BA84D017FDEB3A01F692AF" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_7FC4DEB09A3D6C867E42EB3A01F6A2E3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_EA7C3B69240B214DEC91EB3A01F6B2F0" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8C1674178A3091A1E004EB3A01F52544" xlink:to="loc_us-gaap_AwardTypeAxis_EA7C3B69240B214DEC91EB3A01F6B2F0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19A5101908DF61B92487EB3A01F6BFEA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_EA7C3B69240B214DEC91EB3A01F6B2F0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19A5101908DF61B92487EB3A01F6BFEA_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19A5101908DF61B92487EB3A01F6BFEA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_EA7C3B69240B214DEC91EB3A01F6B2F0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19A5101908DF61B92487EB3A01F6BFEA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_77C6C3075423D9C1E438EB3A01F6148C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_19A5101908DF61B92487EB3A01F6BFEA" xlink:to="loc_us-gaap_RestrictedStockMember_77C6C3075423D9C1E438EB3A01F6148C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_011BD24687413E005C77EB3A01F7E213" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_011BD24687413E005C77EB3A01F7E213" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_D6554CE926F4DEA41A0DEB3A01F77A1F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_D6554CE926F4DEA41A0DEB3A01F77A1F" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationIndemnificationAssetsSharesHeldinEscrow" xlink:label="loc_rubi_BusinessCombinationIndemnificationAssetsSharesHeldinEscrow_CFF3FDC5FD1B75CD9CBCEB3A01F79083" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessCombinationIndemnificationAssetsSharesHeldinEscrow_CFF3FDC5FD1B75CD9CBCEB3A01F79083" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_6713B4F755F7530A6B3BEB3A01F7F5EF" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_6713B4F755F7530A6B3BEB3A01F7F5EF" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationContingentConsiderationThresholdTradingDaystoDetermineNumberofShares" xlink:label="loc_rubi_BusinessCombinationContingentConsiderationThresholdTradingDaystoDetermineNumberofShares_289DB6F9CF18B5C08D48EB3A01F76C01" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessCombinationContingentConsiderationThresholdTradingDaystoDetermineNumberofShares_289DB6F9CF18B5C08D48EB3A01F76C01" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueInputsDiscountRate" xlink:label="loc_us-gaap_FairValueInputsDiscountRate_58EA55E0E053130C6EC6EB3A01F70E42" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_FairValueInputsDiscountRate_58EA55E0E053130C6EC6EB3A01F70E42" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationConsiderationTransferredStockOptionsExchangedandCompensationNotyetRecognized" xlink:label="loc_rubi_BusinessCombinationConsiderationTransferredStockOptionsExchangedandCompensationNotyetRecognized_460D0C3809F7B2662F98EB3A01F7D8C5" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessCombinationConsiderationTransferredStockOptionsExchangedandCompensationNotyetRecognized_460D0C3809F7B2662F98EB3A01F7D8C5" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationConsiderationTransferredStockOptionsExchanged" xlink:label="loc_rubi_BusinessCombinationConsiderationTransferredStockOptionsExchanged_FDB538C1693F61DB4C34EB3A01F74EE9" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessCombinationConsiderationTransferredStockOptionsExchanged_FDB538C1693F61DB4C34EB3A01F74EE9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_B212AA0EE8F72A712FE6EB3A01F79154" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_B212AA0EE8F72A712FE6EB3A01F79154" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_32AC7FA3036CE3952C25EB3A01F7B53A" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_32AC7FA3036CE3952C25EB3A01F7B53A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredTaxAssetsGross" xlink:label="loc_us-gaap_DeferredTaxAssetsGross_08A5702368D4835F3546EB3A01F7F8C0" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_DeferredTaxAssetsGross_08A5702368D4835F3546EB3A01F7F8C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets_1D805CC5522512FFFA1DEB3A01F7516A" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets_1D805CC5522512FFFA1DEB3A01F7516A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredTaxesBusinessCombinationValuationAllowanceAvailableToReduceIncomeTaxExpense" xlink:label="loc_us-gaap_DeferredTaxesBusinessCombinationValuationAllowanceAvailableToReduceIncomeTaxExpense_A6D5A532AC83FBE1FB4DEB3A01F79571" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_DeferredTaxesBusinessCombinationValuationAllowanceAvailableToReduceIncomeTaxExpense_A6D5A532AC83FBE1FB4DEB3A01F79571" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessAcquisitionGoodwillExpectedTaxNondeductibleAmount" xlink:label="loc_rubi_BusinessAcquisitionGoodwillExpectedTaxNondeductibleAmount_C59EBAF437DCE1B1F03DEB3A01F7705A" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessAcquisitionGoodwillExpectedTaxNondeductibleAmount_C59EBAF437DCE1B1F03DEB3A01F7705A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_D52BC4B1E346920F891CEB3A01F7603F" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_D52BC4B1E346920F891CEB3A01F7603F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_000019EF0288DD887772EB3A01F75AA5" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_000019EF0288DD887772EB3A01F75AA5" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationContingentConsiderationSharesIssued" xlink:label="loc_rubi_BusinessCombinationContingentConsiderationSharesIssued_C41B97B189DA041D7387EB3A01F769B5" xlink:type="locator" />
    <definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessCombinationContingentConsiderationSharesIssued_C41B97B189DA041D7387EB3A01F769B5" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationContingentConsiderationEquitytobeRecognizedCurrent" xlink:label="loc_rubi_BusinessCombinationContingentConsiderationEquitytobeRecognizedCurrent_AF4A021F141DE6276481EB3A01F76C7B" xlink:type="locator" />
    <definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_rubi_BusinessCombinationContingentConsiderationEquitytobeRecognizedCurrent_AF4A021F141DE6276481EB3A01F76C7B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_4CDE1758E72265C57008EB3A01F78DF5" xlink:type="locator" />
    <definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_D9C81ED245EA8B04DE32EB3A01F64257" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_4CDE1758E72265C57008EB3A01F78DF5" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BusinessCombinationsProFormaInformationDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_3108E85CC97F83D03927B7D97F29B437" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_CA5535434EF34B418A61B7D97F299DEA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3108E85CC97F83D03927B7D97F29B437" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_CA5535434EF34B418A61B7D97F299DEA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_333B46B94C042DF8B23AB7D97F29362E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_CA5535434EF34B418A61B7D97F299DEA" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_333B46B94C042DF8B23AB7D97F29362E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_B6E59A5DEB215BF990E6B7D97F291308_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_333B46B94C042DF8B23AB7D97F29362E" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_B6E59A5DEB215BF990E6B7D97F291308_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_B6E59A5DEB215BF990E6B7D97F291308" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_333B46B94C042DF8B23AB7D97F29362E" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_B6E59A5DEB215BF990E6B7D97F291308" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ISocketIncandShinyIncMember" xlink:label="loc_rubi_ISocketIncandShinyIncMember_DC47294BDB49031BD607B7D97F29E2E9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_B6E59A5DEB215BF990E6B7D97F291308" xlink:to="loc_rubi_ISocketIncandShinyIncMember_DC47294BDB49031BD607B7D97F29E2E9" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_MobSmithMember" xlink:label="loc_rubi_MobSmithMember_E7E2B4DE4C63F2E4978FB7D97F29EF7D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_B6E59A5DEB215BF990E6B7D97F291308" xlink:to="loc_rubi_MobSmithMember_E7E2B4DE4C63F2E4978FB7D97F29EF7D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_9C56E0257C8769EF64BEB7D97F294E25" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3108E85CC97F83D03927B7D97F29B437" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_9C56E0257C8769EF64BEB7D97F294E25" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_D76A552D85CDC209A6ECB7D97F29FFA0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3108E85CC97F83D03927B7D97F29B437" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_D76A552D85CDC209A6ECB7D97F29FFA0" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/BusinessCombinationsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/Capitalization" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CapitalizationConvertiblePreferredStockDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityLineItems" xlink:label="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityByClassOfStockTable" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_EF1AD36CE0A5B090C1F2BCAD9874A888" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_EF1AD36CE0A5B090C1F2BCAD9874A888" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_AAA2FC25F18054971708BCAD98745A87" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_EF1AD36CE0A5B090C1F2BCAD9874A888" xlink:to="loc_us-gaap_StatementClassOfStockAxis_AAA2FC25F18054971708BCAD98745A87" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_F44813D705CE0A8D567BBCAD98740B90_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_AAA2FC25F18054971708BCAD98745A87" xlink:to="loc_us-gaap_ClassOfStockDomain_F44813D705CE0A8D567BBCAD98740B90_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_F44813D705CE0A8D567BBCAD98740B90" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_AAA2FC25F18054971708BCAD98745A87" xlink:to="loc_us-gaap_ClassOfStockDomain_F44813D705CE0A8D567BBCAD98740B90" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_A5541C5125042179A4ABBCAD987507DB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_F44813D705CE0A8D567BBCAD98740B90" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_A5541C5125042179A4ABBCAD987507DB" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesAConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesAConvertiblePreferredStockMember_6B756BAC69E903E6BBECBCAD98758434" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_A5541C5125042179A4ABBCAD987507DB" xlink:to="loc_rubi_SeriesAConvertiblePreferredStockMember_6B756BAC69E903E6BBECBCAD98758434" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesBConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesBConvertiblePreferredStockMember_8BEDD583FF36791B6342BCAD987585CF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_A5541C5125042179A4ABBCAD987507DB" xlink:to="loc_rubi_SeriesBConvertiblePreferredStockMember_8BEDD583FF36791B6342BCAD987585CF" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesCConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesCConvertiblePreferredStockMember_BCAE6BD7FB103EB7954CBCAD9875C760" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_A5541C5125042179A4ABBCAD987507DB" xlink:to="loc_rubi_SeriesCConvertiblePreferredStockMember_BCAE6BD7FB103EB7954CBCAD9875C760" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesDConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesDConvertiblePreferredStockMember_D9C3A70FB6EA9D0F2296BCAD9875771D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_A5541C5125042179A4ABBCAD987507DB" xlink:to="loc_rubi_SeriesDConvertiblePreferredStockMember_D9C3A70FB6EA9D0F2296BCAD9875771D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_AE6D27020C9873FD0C70BCAD987BD093" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_AE6D27020C9873FD0C70BCAD987BD093" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_A13FC498BADF55B6348ABCAD987D2387" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_A13FC498BADF55B6348ABCAD987D2387" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_98E1B7FCBEA0AFF83C3CBCAD987D4414" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_98E1B7FCBEA0AFF83C3CBCAD987D4414" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityLiquidationPreference" xlink:label="loc_us-gaap_TemporaryEquityLiquidationPreference_95E691F033C795FF0D70BCAD987DF201" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_us-gaap_TemporaryEquityLiquidationPreference_95E691F033C795FF0D70BCAD987DF201" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_TemporaryEquityIssuancePricePerShare" xlink:label="loc_rubi_TemporaryEquityIssuancePricePerShare_6E2A7DA66A81FEA7A3A5BCAD987D3A85" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_rubi_TemporaryEquityIssuancePricePerShare_6E2A7DA66A81FEA7A3A5BCAD987D3A85" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:label="loc_us-gaap_TemporaryEquityRedemptionPricePerShare_804A6F2CBBEDE984298ABCAD987D90FB" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_18BCB2CAB0E7F44851B7BCAD98753BD9" xlink:to="loc_us-gaap_TemporaryEquityRedemptionPricePerShare_804A6F2CBBEDE984298ABCAD987D90FB" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CapitalizationNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_186D07D256AB4246F5C0E7CD7847398A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_186D07D256AB4246F5C0E7CD7847398A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_ACFD9FFBD3B93F906607E7CD7848FD6F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_186D07D256AB4246F5C0E7CD7847398A" xlink:to="loc_us-gaap_StatementClassOfStockAxis_ACFD9FFBD3B93F906607E7CD7848FD6F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ACFD9FFBD3B93F906607E7CD7848FD6F" xlink:to="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ACFD9FFBD3B93F906607E7CD7848FD6F" xlink:to="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_B43670C59623679698DAE7CD78488242" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:to="loc_us-gaap_CommonClassAMember_B43670C59623679698DAE7CD78488242" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_B4AE11D42860FA25B39EE7CD784906F6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:to="loc_us-gaap_CommonClassBMember_B4AE11D42860FA25B39EE7CD784906F6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_12027B90ACE3F0D353CFE7CD7849D9EC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:to="loc_us-gaap_CommonStockMember_12027B90ACE3F0D353CFE7CD7849D9EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_B1050CF22CD11C23718AE7CD78491D50" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_B1050CF22CD11C23718AE7CD78491D50" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesAConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesAConvertiblePreferredStockMember_D889A57ED84E2BAB40E0E7CD784909F8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_B1050CF22CD11C23718AE7CD78491D50" xlink:to="loc_rubi_SeriesAConvertiblePreferredStockMember_D889A57ED84E2BAB40E0E7CD784909F8" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesBConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesBConvertiblePreferredStockMember_878BCBBCBD33B54C0383E7CD78498CE4" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_B1050CF22CD11C23718AE7CD78491D50" xlink:to="loc_rubi_SeriesBConvertiblePreferredStockMember_878BCBBCBD33B54C0383E7CD78498CE4" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesCConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesCConvertiblePreferredStockMember_2574D5D8056949F2473FE7CD784A425E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_B1050CF22CD11C23718AE7CD78491D50" xlink:to="loc_rubi_SeriesCConvertiblePreferredStockMember_2574D5D8056949F2473FE7CD784A425E" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesDConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesDConvertiblePreferredStockMember_ECD8A5861AE9A4ACE205E7CD784ABDB8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConvertiblePreferredStockMember_B1050CF22CD11C23718AE7CD78491D50" xlink:to="loc_rubi_SeriesDConvertiblePreferredStockMember_ECD8A5861AE9A4ACE205E7CD784ABDB8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_E128111D77606FBA86CDE7CD784AD8F1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B89DC8B97B4370E43981E7CD78489F3E" xlink:to="loc_us-gaap_PreferredStockMember_E128111D77606FBA86CDE7CD784AD8F1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_6B506A4F48D2AEE05430E7CD784AC692" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_186D07D256AB4246F5C0E7CD7847398A" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_6B506A4F48D2AEE05430E7CD784AC692" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_54771BB2D6DD8CE440FEE7CD784A7E71_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_6B506A4F48D2AEE05430E7CD784AC692" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_54771BB2D6DD8CE440FEE7CD784A7E71_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_54771BB2D6DD8CE440FEE7CD784A7E71" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_6B506A4F48D2AEE05430E7CD784AC692" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_54771BB2D6DD8CE440FEE7CD784A7E71" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_9DA1B20FFC6F497E8EF2E7CD784A1F05" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_54771BB2D6DD8CE440FEE7CD784A7E71" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_9DA1B20FFC6F497E8EF2E7CD784A1F05" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_3CA90E29220360BEAF7EE7CD784B20D6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_54771BB2D6DD8CE440FEE7CD784A7E71" xlink:to="loc_us-gaap_CommonStockMember_3CA90E29220360BEAF7EE7CD784B20D6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_7C641D718443EB639695E7CD784B07BD" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_186D07D256AB4246F5C0E7CD7847398A" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_7C641D718443EB639695E7CD784B07BD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_0905FA2B3B04D50E55A1E7CD784BAEC6_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7C641D718443EB639695E7CD784B07BD" xlink:to="loc_us-gaap_EquityComponentDomain_0905FA2B3B04D50E55A1E7CD784BAEC6_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_0905FA2B3B04D50E55A1E7CD784BAEC6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7C641D718443EB639695E7CD784B07BD" xlink:to="loc_us-gaap_EquityComponentDomain_0905FA2B3B04D50E55A1E7CD784BAEC6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_749AF8132E5F9532EC0FE7CD784B29D2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0905FA2B3B04D50E55A1E7CD784BAEC6" xlink:to="loc_us-gaap_CommonStockMember_749AF8132E5F9532EC0FE7CD784B29D2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_0259ED00924E7C70E658E7CD784CF71D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_0259ED00924E7C70E658E7CD784CF71D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_687DCC8425B3EB4E3C1DE7CD784C2AB5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_687DCC8425B3EB4E3C1DE7CD784C2AB5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_F6E6D6382C370F79972AE7CD784C1C28" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_F6E6D6382C370F79972AE7CD784C1C28" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_InitialPublicOfferingSharessoldDuringIPOOverAllotmentOption" xlink:label="loc_rubi_InitialPublicOfferingSharessoldDuringIPOOverAllotmentOption_792A9967D5FAF160BC28E7CD784C719E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_InitialPublicOfferingSharessoldDuringIPOOverAllotmentOption_792A9967D5FAF160BC28E7CD784C719E" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_InitialPublicOfferingSharesSoldbyExistingStockholders" xlink:label="loc_rubi_InitialPublicOfferingSharesSoldbyExistingStockholders_D46D4C061CBA25F7113EE7CD784C3E76" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_InitialPublicOfferingSharesSoldbyExistingStockholders_D46D4C061CBA25F7113EE7CD784C3E76" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaap_SharePrice_CC4923B2BAFFEB77602DE7CD784C52B8" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_SharePrice_CC4923B2BAFFEB77602DE7CD784C52B8" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ProceedsfromIssuanceInitialPublicOfferingNetofOfferingCosts" xlink:label="loc_rubi_ProceedsfromIssuanceInitialPublicOfferingNetofOfferingCosts_99D1B30F112A2CE6D097E7CD784C2E51" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_ProceedsfromIssuanceInitialPublicOfferingNetofOfferingCosts_99D1B30F112A2CE6D097E7CD784C2E51" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_8EB2BB3C20164B0D3E03E7CD784CE9ED" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_8EB2BB3C20164B0D3E03E7CD784CE9ED" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_883E9B033D2EF32753D8E7CD784D3DA1" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_883E9B033D2EF32753D8E7CD784D3DA1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_7D197DAFE725169FD957E7CD784DE51D" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_7D197DAFE725169FD957E7CD784DE51D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_2E3FB0B8B20F8BC825AFE7CD784DABFE" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_2E3FB0B8B20F8BC825AFE7CD784DABFE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_360EC83CB78E88F8EE14E7CD784D554C" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_360EC83CB78E88F8EE14E7CD784D554C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_A269B987DBC81171BDF4E7CD784DDA39" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_A269B987DBC81171BDF4E7CD784DDA39" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredOfferingCosts" xlink:label="loc_us-gaap_DeferredOfferingCosts_8174227ACC81F5CF7E03E7CD784D70F2" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_DeferredOfferingCosts_8174227ACC81F5CF7E03E7CD784D70F2" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_TemporaryEquityDividendRatePerDollarAmount" xlink:label="loc_rubi_TemporaryEquityDividendRatePerDollarAmount_EA93C4D80A24750C7C31E7CD784D1BBA" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_TemporaryEquityDividendRatePerDollarAmount_EA93C4D80A24750C7C31E7CD784D1BBA" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_TemporaryEquityAmountofPreferredDividendsinArrears" xlink:label="loc_rubi_TemporaryEquityAmountofPreferredDividendsinArrears_F7BEE231B7E4B25B033DE7CD784D8116" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_TemporaryEquityAmountofPreferredDividendsinArrears_F7BEE231B7E4B25B033DE7CD784D8116" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ConvertiblePreferredStockTermsofConversionProceedsfromIssuanceInitialPublicOfferingNetofOfferingCostsMinimum" xlink:label="loc_rubi_ConvertiblePreferredStockTermsofConversionProceedsfromIssuanceInitialPublicOfferingNetofOfferingCostsMinimum_16B2A1F542CFF3224E27E7CD784E69AF" xlink:type="locator" />
    <definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_ConvertiblePreferredStockTermsofConversionProceedsfromIssuanceInitialPublicOfferingNetofOfferingCostsMinimum_16B2A1F542CFF3224E27E7CD784E69AF" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ConvertiblePreferredStockTermsofConversionPreOfferingEnterpriseValueMinimum" xlink:label="loc_rubi_ConvertiblePreferredStockTermsofConversionPreOfferingEnterpriseValueMinimum_9E054E12E750D9ACD1A7E7CD784EE251" xlink:type="locator" />
    <definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_ConvertiblePreferredStockTermsofConversionPreOfferingEnterpriseValueMinimum_9E054E12E750D9ACD1A7E7CD784EE251" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ConvertiblePreferredStockTermsofConversionHolderConsentVotePercentMinimum" xlink:label="loc_rubi_ConvertiblePreferredStockTermsofConversionHolderConsentVotePercentMinimum_2A07B964C0E43ED95820E7CD784E7273" xlink:type="locator" />
    <definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_ConvertiblePreferredStockTermsofConversionHolderConsentVotePercentMinimum_2A07B964C0E43ED95820E7CD784E7273" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_9B9D80187203760AC995E7CD784EA89E" xlink:type="locator" />
    <definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_9B9D80187203760AC995E7CD784EA89E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_DA9959A7FBC704913A92E7CD784E0E8F" xlink:type="locator" />
    <definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_DA9959A7FBC704913A92E7CD784E0E8F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_91498F93AB4F17A1DD1FE7CD784E0794" xlink:type="locator" />
    <definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_91498F93AB4F17A1DD1FE7CD784E0794" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_D08688A4DFF1D00CC074E7CD784F4B27" xlink:type="locator" />
    <definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_D08688A4DFF1D00CC074E7CD784F4B27" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_BusinessCombinationContingentConsiderationThresholdTradingDaystoDetermineNumberofShares" xlink:label="loc_rubi_BusinessCombinationContingentConsiderationThresholdTradingDaystoDetermineNumberofShares_0D5006790007048D89B6E7CD784F866A" xlink:type="locator" />
    <definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6E63B91DD4C2AD034EAAE7CD784BDE38" xlink:to="loc_rubi_BusinessCombinationContingentConsiderationThresholdTradingDaystoDetermineNumberofShares_0D5006790007048D89B6E7CD784F866A" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CapitalizationTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CommitmentsAndContingenciesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CommitmentsAndContingenciesOperatingLeasesFutureMinimumPaymentsDueDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CommitmentsAndContingenciesOtherContractsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_5A9F392B4816E547767363F4E5E471F9" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_668AD3C4B9595B0F9EC563F4E5E35349" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_5A9F392B4816E547767363F4E5E471F9" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_668AD3C4B9595B0F9EC563F4E5E35349" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_1F3892D87F3C61CD142263F4E5E38166" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_668AD3C4B9595B0F9EC563F4E5E35349" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_1F3892D87F3C61CD142263F4E5E38166" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_F7B9C13F0C50A797FC5863F4E5E3E643_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_1F3892D87F3C61CD142263F4E5E38166" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_F7B9C13F0C50A797FC5863F4E5E3E643_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_F7B9C13F0C50A797FC5863F4E5E3E643" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_1F3892D87F3C61CD142263F4E5E38166" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_F7B9C13F0C50A797FC5863F4E5E3E643" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesCConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesCConvertiblePreferredStockMember_5F697EAFB4F936803C4F63F4E5E3FF36" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_F7B9C13F0C50A797FC5863F4E5E3E643" xlink:to="loc_rubi_SeriesCConvertiblePreferredStockMember_5F697EAFB4F936803C4F63F4E5E3FF36" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_8AAF272A4A9C6A4B6DF163F4E5E4D470" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_F7B9C13F0C50A797FC5863F4E5E3E643" xlink:to="loc_us-gaap_CommonStockMember_8AAF272A4A9C6A4B6DF163F4E5E4D470" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_B8885459977A1E7C929063F4E5E47B4B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_668AD3C4B9595B0F9EC563F4E5E35349" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_B8885459977A1E7C929063F4E5E47B4B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_6733BB41DD6EA4250E2063F4E5E418C4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_B8885459977A1E7C929063F4E5E47B4B" xlink:to="loc_us-gaap_EquityComponentDomain_6733BB41DD6EA4250E2063F4E5E418C4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_6733BB41DD6EA4250E2063F4E5E418C4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_B8885459977A1E7C929063F4E5E47B4B" xlink:to="loc_us-gaap_EquityComponentDomain_6733BB41DD6EA4250E2063F4E5E418C4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_E0EB3DA3982C294F8CBA63F4E5E43518" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_6733BB41DD6EA4250E2063F4E5E418C4" xlink:to="loc_us-gaap_CommonStockMember_E0EB3DA3982C294F8CBA63F4E5E43518" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_B637A241FFC95F77AE6863F4E5E480E5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5A9F392B4816E547767363F4E5E471F9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_B637A241FFC95F77AE6863F4E5E480E5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_39BA1E259662C759280463F4E5E4AA62" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5A9F392B4816E547767363F4E5E471F9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_39BA1E259662C759280463F4E5E4AA62" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_F0CA801AF362635F6C5A63F4E5E462D3" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5A9F392B4816E547767363F4E5E471F9" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_F0CA801AF362635F6C5A63F4E5E462D3" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_AcquisitionFeePercentageofConsiderationDue" xlink:label="loc_rubi_AcquisitionFeePercentageofConsiderationDue_02ECF4454E4F47834C8963F4E5E448B5" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5A9F392B4816E547767363F4E5E471F9" xlink:to="loc_rubi_AcquisitionFeePercentageofConsiderationDue_02ECF4454E4F47834C8963F4E5E448B5" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/CommitmentsAndContingenciesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/ConsolidatedBalanceSheets" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_5846DA15C4B3E8FD4E0AC6D9E71BB166" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_StatementTable_5846DA15C4B3E8FD4E0AC6D9E71BB166" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_02E8AD6C65EC407CFFC0C6D9E71B126D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_5846DA15C4B3E8FD4E0AC6D9E71BB166" xlink:to="loc_us-gaap_StatementClassOfStockAxis_02E8AD6C65EC407CFFC0C6D9E71B126D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_544B74E93BD876899C3AC6D9E71B1A46_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_02E8AD6C65EC407CFFC0C6D9E71B126D" xlink:to="loc_us-gaap_ClassOfStockDomain_544B74E93BD876899C3AC6D9E71B1A46_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_544B74E93BD876899C3AC6D9E71B1A46" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_02E8AD6C65EC407CFFC0C6D9E71B126D" xlink:to="loc_us-gaap_ClassOfStockDomain_544B74E93BD876899C3AC6D9E71B1A46" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_AD8D15F490C912A17A9DC6D9E71B7D11" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_544B74E93BD876899C3AC6D9E71B1A46" xlink:to="loc_us-gaap_PreferredStockMember_AD8D15F490C912A17A9DC6D9E71B7D11" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_736F813956FCEED583C4C6D9E71B4BDC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_544B74E93BD876899C3AC6D9E71B1A46" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_736F813956FCEED583C4C6D9E71B4BDC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_152862E8A90493561555C6D9E71C8D64" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_152862E8A90493561555C6D9E71C8D64" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_4EB237A8151492F071E3C6D9E71C9227" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_4EB237A8151492F071E3C6D9E71C9227" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_3D22AC69AC084506A601C6D9E71C0A83" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_3D22AC69AC084506A601C6D9E71C0A83" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesAuthorized" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_4AB5D478872623836A22C6D9E71C7182" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_4AB5D478872623836A22C6D9E71C7182" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_41C92D5A5627405F4838C6D9E71C47B7" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_41C92D5A5627405F4838C6D9E71C47B7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_76B029E4A2119D072D23C6D9E71C4579" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CE3332599314940BF960C6D9E71C8E56" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_76B029E4A2119D072D23C6D9E71C4579" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/ConsolidatedStatementOfCashFlows" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/ConsolidatedStatementOfComprehensiveLoss" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/ConsolidatedStatementOfConvertiblePreferredStockAndStockholdersEquityDeficit" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_592775929B2969B696BCE2889AE83509" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_387CF52465E7DC8CC25DE2889AE14772" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_592775929B2969B696BCE2889AE83509" xlink:to="loc_us-gaap_StatementTable_387CF52465E7DC8CC25DE2889AE14772" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_69B6FD31B493909645B4E2889AE1A4F7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_387CF52465E7DC8CC25DE2889AE14772" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_69B6FD31B493909645B4E2889AE1A4F7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_69B6FD31B493909645B4E2889AE1A4F7" xlink:to="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_69B6FD31B493909645B4E2889AE1A4F7" xlink:to="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_C7D2FFA5F14E09271A59E2889AE78A35" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:to="loc_us-gaap_PreferredStockMember_C7D2FFA5F14E09271A59E2889AE78A35" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_00398D9124B6677C1FE6E2889AE74066" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:to="loc_us-gaap_CommonStockMember_00398D9124B6677C1FE6E2889AE74066" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_8E964331C0DB9CB0C994E2889AE768FF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_8E964331C0DB9CB0C994E2889AE768FF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_D6C1C4A229C043972A1DE2889AE7536A" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_D6C1C4A229C043972A1DE2889AE7536A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_0DF6A12F1D2FFFFD8D6AE2889AE7CC46" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D3819AD7187EA42F1FC5E2889AE22EB2" xlink:to="loc_us-gaap_RetainedEarningsMember_0DF6A12F1D2FFFFD8D6AE2889AE7CC46" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_592775929B2969B696BCE2889AE83509" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_83142733ADFCF0B7EE9CE2889AE8CE02" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_83142733ADFCF0B7EE9CE2889AE8CE02" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_2E2B14F4BECF9D873AEDE2889AE8661D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_2E2B14F4BECF9D873AEDE2889AE8661D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_EEC84FCBF6F2B455DFDFE2889AE843D4" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_EEC84FCBF6F2B455DFDFE2889AE843D4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_B62243654A258E161F8BE2889AE8A4F0" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockholdersEquity_B62243654A258E161F8BE2889AE8A4F0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_AA6E6EA11858F2B69A77E2889AE83591" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_AA6E6EA11858F2B69A77E2889AE83591" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_D04F2DD63BDF2AE3B422E2889AE89A22" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_D04F2DD63BDF2AE3B422E2889AE89A22" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_884E228F0A10181B4B81E2889AE8CF9B" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_884E228F0A10181B4B81E2889AE8CF9B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_F922AFF38C09AA0105ACE2889AE87F9A" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_F922AFF38C09AA0105ACE2889AE87F9A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_26AE84D4CB6B77C3E6C4E2889AE94923" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_26AE84D4CB6B77C3E6C4E2889AE94923" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_5186BDDC0AA01638BDEBE2889AE90DD4" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_5186BDDC0AA01638BDEBE2889AE90DD4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AdjustmentToAdditionalPaidInCapitalIncomeTaxEffectFromShareBasedCompensationNet" xlink:label="loc_us-gaap_AdjustmentToAdditionalPaidInCapitalIncomeTaxEffectFromShareBasedCompensationNet_96D7CA6D263E999B8E3FE2889AE9C1AE" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_AdjustmentToAdditionalPaidInCapitalIncomeTaxEffectFromShareBasedCompensationNet_96D7CA6D263E999B8E3FE2889AE9C1AE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_1C6AC08FFADE963D9455E298006CEBC3" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_1C6AC08FFADE963D9455E298006CEBC3" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_StockIssuedDuringPeriodSharesStockWarrantsNetExercised" xlink:label="loc_rubi_StockIssuedDuringPeriodSharesStockWarrantsNetExercised_28AFAB52C7C196DAEBF1E2889AE9C3BA" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_rubi_StockIssuedDuringPeriodSharesStockWarrantsNetExercised_28AFAB52C7C196DAEBF1E2889AE9C3BA" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_StockIssuedDuringPeriodValueStockWarrantsNetExercised" xlink:label="loc_rubi_StockIssuedDuringPeriodValueStockWarrantsNetExercised_1B544C25622C37777C1DE2889AE92511" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_rubi_StockIssuedDuringPeriodValueStockWarrantsNetExercised_1B544C25622C37777C1DE2889AE92511" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_4192D86BCF9FDD9D6611E2889AE9BB49" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_4192D86BCF9FDD9D6611E2889AE9BB49" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_0F9FC14ABFE3B82D1644E2889AE9F167" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_0F9FC14ABFE3B82D1644E2889AE9F167" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_6E6D79A5608B53D15BBBE2889AE91B94" xlink:type="locator" />
    <definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_6E6D79A5608B53D15BBBE2889AE91B94" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_ED3859A145F93534E819E2889AE92064" xlink:type="locator" />
    <definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_ED3859A145F93534E819E2889AE92064" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_7C1EC479358C1CF645C2E2889AE9B0C0" xlink:type="locator" />
    <definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_7C1EC479358C1CF645C2E2889AE9B0C0" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_NetExerciseOfWarrantSharesCommonStock" xlink:label="loc_rubi_NetExerciseOfWarrantSharesCommonStock_16C7DF109A088948FA72E2889AEA8B3F" xlink:type="locator" />
    <definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_rubi_NetExerciseOfWarrantSharesCommonStock_16C7DF109A088948FA72E2889AEA8B3F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_1FCEFF9EA90B84F153A9E2889AEA237D" xlink:type="locator" />
    <definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_1FCEFF9EA90B84F153A9E2889AEA237D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_F82FBC21F0F7CC4206E4E2889AEAF882" xlink:type="locator" />
    <definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_F82FBC21F0F7CC4206E4E2889AEAF882" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_DAB5DAD26C3DA7F942C0E2889AEAD6A5" xlink:type="locator" />
    <definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_DAB5DAD26C3DA7F942C0E2889AEAD6A5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_B1B6E237ED1E6B8AA41BE2889AEA7D7C" xlink:type="locator" />
    <definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2487C253F6117448446CE2889AE81AF9" xlink:to="loc_us-gaap_NetIncomeLoss_B1B6E237ED1E6B8AA41BE2889AEA7D7C" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/ConsolidatedStatementOfOperations" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangements" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangementsDebtAndCapitalLeaseArrangementsDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangementsNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_C6B601BC51FF2EBD367EEC65AC1717C6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_C6B601BC51FF2EBD367EEC65AC1717C6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_334349EAD9B835537B18EC65AC172E2E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_C6B601BC51FF2EBD367EEC65AC1717C6" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_334349EAD9B835537B18EC65AC172E2E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_334349EAD9B835537B18EC65AC172E2E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_C6B601BC51FF2EBD367EEC65AC1717C6" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_334349EAD9B835537B18EC65AC172E2E" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SiliconValleyBankMember" xlink:label="loc_rubi_SiliconValleyBankMember_E09B51746848FFD67380EC65AC179C1D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_334349EAD9B835537B18EC65AC172E2E" xlink:to="loc_rubi_SiliconValleyBankMember_E09B51746848FFD67380EC65AC179C1D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_4626915A360DD7544A2DEC65AC170C86" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_4626915A360DD7544A2DEC65AC170C86" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_952B849CF26299A87C7BEC65AC1752A6_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4626915A360DD7544A2DEC65AC170C86" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_952B849CF26299A87C7BEC65AC1752A6_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_952B849CF26299A87C7BEC65AC1752A6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4626915A360DD7544A2DEC65AC170C86" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_952B849CF26299A87C7BEC65AC1752A6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditMember" xlink:label="loc_us-gaap_LineOfCreditMember_B011CDD259CD8C0ED6E7EC65AC178110" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_952B849CF26299A87C7BEC65AC1752A6" xlink:to="loc_us-gaap_LineOfCreditMember_B011CDD259CD8C0ED6E7EC65AC178110" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_D5AFFBA59A89F3199BCAEC65AC18C6B6" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:to="loc_us-gaap_CreditFacilityAxis_D5AFFBA59A89F3199BCAEC65AC18C6B6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_FAE28EAC508E04C964EBEC65AC18ABF1_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_D5AFFBA59A89F3199BCAEC65AC18C6B6" xlink:to="loc_us-gaap_CreditFacilityDomain_FAE28EAC508E04C964EBEC65AC18ABF1_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_FAE28EAC508E04C964EBEC65AC18ABF1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_D5AFFBA59A89F3199BCAEC65AC18C6B6" xlink:to="loc_us-gaap_CreditFacilityDomain_FAE28EAC508E04C964EBEC65AC18ABF1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_475CCAA19017A51E0318EC65AC188237" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_FAE28EAC508E04C964EBEC65AC18ABF1" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_475CCAA19017A51E0318EC65AC188237" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_37D17102FCC52DC2D82DEC65AC187F19" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:to="loc_us-gaap_DebtInstrumentAxis_37D17102FCC52DC2D82DEC65AC187F19" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_078E462ECC2C393EDD72EC65AC18388E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_37D17102FCC52DC2D82DEC65AC187F19" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_078E462ECC2C393EDD72EC65AC18388E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_078E462ECC2C393EDD72EC65AC18388E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_37D17102FCC52DC2D82DEC65AC187F19" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_078E462ECC2C393EDD72EC65AC18388E" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_A2011LoanAgreementMember" xlink:label="loc_rubi_A2011LoanAgreementMember_6F61FA38AF94070AC7E4EC65AC186FD2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_078E462ECC2C393EDD72EC65AC18388E" xlink:to="loc_rubi_A2011LoanAgreementMember_6F61FA38AF94070AC7E4EC65AC186FD2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_E32354FC09C2BBFB57E3EC65AC1827CD" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:to="loc_us-gaap_VariableRateAxis_E32354FC09C2BBFB57E3EC65AC1827CD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_6BCAC9FBA41CAF91805DEC65AC19F144_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_E32354FC09C2BBFB57E3EC65AC1827CD" xlink:to="loc_us-gaap_VariableRateDomain_6BCAC9FBA41CAF91805DEC65AC19F144_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_6BCAC9FBA41CAF91805DEC65AC19F144" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_E32354FC09C2BBFB57E3EC65AC1827CD" xlink:to="loc_us-gaap_VariableRateDomain_6BCAC9FBA41CAF91805DEC65AC19F144" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PrimeRateMember" xlink:label="loc_us-gaap_PrimeRateMember_CF7804547FBDA188CBE1EC65AC19EBAB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_6BCAC9FBA41CAF91805DEC65AC19F144" xlink:to="loc_us-gaap_PrimeRateMember_CF7804547FBDA188CBE1EC65AC19EBAB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_6622867BC948B5E97576EC65AC19238C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_6BCAC9FBA41CAF91805DEC65AC19F144" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_6622867BC948B5E97576EC65AC19238C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_659593DE99A7A49C1D1EEC65AC19CE83" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_8C7AEE07B495F2A1AB71EC65AC1741E5" xlink:to="loc_us-gaap_StatementScenarioAxis_659593DE99A7A49C1D1EEC65AC19CE83" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_33D565C0B558BE54CEEEEC65AC196AE8_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_659593DE99A7A49C1D1EEC65AC19CE83" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_33D565C0B558BE54CEEEEC65AC196AE8_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_33D565C0B558BE54CEEEEC65AC196AE8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_659593DE99A7A49C1D1EEC65AC19CE83" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_33D565C0B558BE54CEEEEC65AC196AE8" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_NetCashBalanceExceedingOneDollarMaintainedMember" xlink:label="loc_rubi_NetCashBalanceExceedingOneDollarMaintainedMember_EDFFC80DE507B1B6C88AEC65AC19A838" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_33D565C0B558BE54CEEEEC65AC196AE8" xlink:to="loc_rubi_NetCashBalanceExceedingOneDollarMaintainedMember_EDFFC80DE507B1B6C88AEC65AC19A838" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_NetCashBalanceExceedingOneDollarNotMaintainedMember" xlink:label="loc_rubi_NetCashBalanceExceedingOneDollarNotMaintainedMember_45B39F94991572819E78EC65AC19432D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_33D565C0B558BE54CEEEEC65AC196AE8" xlink:to="loc_rubi_NetCashBalanceExceedingOneDollarNotMaintainedMember_45B39F94991572819E78EC65AC19432D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_B541B53B90BB7B0CAF73EC65AC19BE0A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_B541B53B90BB7B0CAF73EC65AC19BE0A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_DDE6124727136F6264EAEC65AC193EFF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_DDE6124727136F6264EAEC65AC193EFF" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_DebtInstrumentMinimumNetCashBalanceBeforeIncreaseinVariableRate" xlink:label="loc_rubi_DebtInstrumentMinimumNetCashBalanceBeforeIncreaseinVariableRate_AB0C51E6092BE7338E1DEC65AC19BD6A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_rubi_DebtInstrumentMinimumNetCashBalanceBeforeIncreaseinVariableRate_AB0C51E6092BE7338E1DEC65AC19BD6A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_E929888FFE6BDDED7AC2EC65AC1A0941" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_E929888FFE6BDDED7AC2EC65AC1A0941" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_DebtInstrumentCovenantMinimumFixedChargeCoverageRatio" xlink:label="loc_rubi_DebtInstrumentCovenantMinimumFixedChargeCoverageRatio_B2845943F06C5F51626AEC65AC1A06FE" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_rubi_DebtInstrumentCovenantMinimumFixedChargeCoverageRatio_B2845943F06C5F51626AEC65AC1A06FE" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_DebtInstrumentCovenantFixedChargeCoverageRatioCalculationPeriod" xlink:label="loc_rubi_DebtInstrumentCovenantFixedChargeCoverageRatioCalculationPeriod_E3363B3C2A5B087147BFEC65AC1A5F53" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_rubi_DebtInstrumentCovenantFixedChargeCoverageRatioCalculationPeriod_E3363B3C2A5B087147BFEC65AC1A5F53" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_B92130D2B365236D70A0EC65AC1AB077" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_B92130D2B365236D70A0EC65AC1AB077" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LineOfCredit" xlink:label="loc_us-gaap_LineOfCredit_9E51F77B9D1706ACB15FEC65AC1A1318" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_LineOfCredit_9E51F77B9D1706ACB15FEC65AC1A1318" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_DebtInstrumentCovenantMinimumRemainingBorrowingCapacityThresholdPercent" xlink:label="loc_rubi_DebtInstrumentCovenantMinimumRemainingBorrowingCapacityThresholdPercent_644282432BB9A4302103EC65AC1A16DD" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_rubi_DebtInstrumentCovenantMinimumRemainingBorrowingCapacityThresholdPercent_644282432BB9A4302103EC65AC1A16DD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RepaymentsOfLinesOfCredit" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_24A668C7C58B78971091EC65AC1A3841" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_24A668C7C58B78971091EC65AC1A3841" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="loc_us-gaap_DebtInstrumentMaturityDate_50C003A1BCC56BF9E562EC65AC1A4462" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_E409AA7F0930A43A6E0DEC65AC19D2FB" xlink:to="loc_us-gaap_DebtInstrumentMaturityDate_50C003A1BCC56BF9E562EC65AC1A4462" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/DebtAndCapitalLeaseArrangementsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/FairValueMeasurements" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/FairValueMeasurementsChangeInFairValueDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_E3859900635C794893F5C3447C647443" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_57A3CB5ED325A247CECFC3447C64DBE1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_E3859900635C794893F5C3447C647443" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_57A3CB5ED325A247CECFC3447C64DBE1" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_5E1BAE09D4C227A93429C3447C641B92" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_57A3CB5ED325A247CECFC3447C64DBE1" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_5E1BAE09D4C227A93429C3447C641B92" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9D4CD2464DDFCF00BC25C3447C647DD4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_5E1BAE09D4C227A93429C3447C641B92" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9D4CD2464DDFCF00BC25C3447C647DD4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9D4CD2464DDFCF00BC25C3447C647DD4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_5E1BAE09D4C227A93429C3447C641B92" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9D4CD2464DDFCF00BC25C3447C647DD4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_WarrantMember" xlink:label="loc_us-gaap_WarrantMember_CEBEEB3501A5A3A0BF0FC3447C6478C0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_9D4CD2464DDFCF00BC25C3447C647DD4" xlink:to="loc_us-gaap_WarrantMember_CEBEEB3501A5A3A0BF0FC3447C6478C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_52FDA375D841A13377E7C3447C64BCFA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_E3859900635C794893F5C3447C647443" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_52FDA375D841A13377E7C3447C64BCFA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_D05C8F2D39FEE38B4B42C3447C65DA44" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_52FDA375D841A13377E7C3447C64BCFA" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_D05C8F2D39FEE38B4B42C3447C65DA44" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_D89968DB5E16A5A56ECBC3447C651E25" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_52FDA375D841A13377E7C3447C64BCFA" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_D89968DB5E16A5A56ECBC3447C651E25" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityConversionofWarrantstoStock" xlink:label="loc_rubi_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityConversionofWarrantstoStock_E879AE6B3643B8678ED9C3447C652DE9" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_52FDA375D841A13377E7C3447C64BCFA" xlink:to="loc_rubi_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityConversionofWarrantstoStock_E879AE6B3643B8678ED9C3447C652DE9" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/FairValueMeasurementsFinancialInstrumentsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_FE05EA1C09E1E1E773BA99D8E3474DEA" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_AAC7FF2E7F9554CF4BEE99D8E346831A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_FE05EA1C09E1E1E773BA99D8E3474DEA" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_AAC7FF2E7F9554CF4BEE99D8E346831A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_0E30D3C1A275AE34662B99D8E346BD39" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_AAC7FF2E7F9554CF4BEE99D8E346831A" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_0E30D3C1A275AE34662B99D8E346BD39" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_CDF807AD35B9976AFE0E99D8E346787E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_0E30D3C1A275AE34662B99D8E346BD39" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_CDF807AD35B9976AFE0E99D8E346787E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_CDF807AD35B9976AFE0E99D8E346787E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_0E30D3C1A275AE34662B99D8E346BD39" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_CDF807AD35B9976AFE0E99D8E346787E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_86E62A2EEC508A3F8E8E99D8E346C536" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_CDF807AD35B9976AFE0E99D8E346787E" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_86E62A2EEC508A3F8E8E99D8E346C536" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_D07F3752CBF8CA518BBC99D8E347EFA2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_AAC7FF2E7F9554CF4BEE99D8E346831A" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_D07F3752CBF8CA518BBC99D8E347EFA2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_D07F3752CBF8CA518BBC99D8E347EFA2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_D07F3752CBF8CA518BBC99D8E347EFA2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_AB3CBE1041FB97D6513199D8E34746AF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_AB3CBE1041FB97D6513199D8E34746AF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_379795C6A58BE4A66E5B99D8E3477583" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_379795C6A58BE4A66E5B99D8E3477583" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_4563A5185A0F655DA37B99D8E347F011" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2F9CEDE9448E0E7130CF99D8E34799C7" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_4563A5185A0F655DA37B99D8E347F011" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_FD1C26DF702AF25B0FDB99D8E3474C13" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_FE05EA1C09E1E1E773BA99D8E3474DEA" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_FD1C26DF702AF25B0FDB99D8E3474C13" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_AC09966D6B46848B94E59A4A30B7579F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_FE05EA1C09E1E1E773BA99D8E3474DEA" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_AC09966D6B46848B94E59A4A30B7579F" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ConvertiblePreferredStockWarrantsFairValueDisclosure" xlink:label="loc_rubi_ConvertiblePreferredStockWarrantsFairValueDisclosure_CC9B386EFFAA45D8FFB299D8E3485CAB" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_FE05EA1C09E1E1E773BA99D8E3474DEA" xlink:to="loc_rubi_ConvertiblePreferredStockWarrantsFairValueDisclosure_CC9B386EFFAA45D8FFB299D8E3485CAB" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/FairValueMeasurementsNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_44174983EBC4CA2E678CE28899A76D77" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_44174983EBC4CA2E678CE28899A76D77" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_31732EEF74B440F37188E28899A783FF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_44174983EBC4CA2E678CE28899A76D77" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_31732EEF74B440F37188E28899A783FF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_ABB31CDD9E787E3A738EE28899A893AD_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_31732EEF74B440F37188E28899A783FF" xlink:to="loc_us-gaap_EquityComponentDomain_ABB31CDD9E787E3A738EE28899A893AD_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_ABB31CDD9E787E3A738EE28899A893AD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_31732EEF74B440F37188E28899A783FF" xlink:to="loc_us-gaap_EquityComponentDomain_ABB31CDD9E787E3A738EE28899A893AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_50CC34B7B73769BF9B80E28899A8C814" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_ABB31CDD9E787E3A738EE28899A893AD" xlink:to="loc_us-gaap_CommonStockMember_50CC34B7B73769BF9B80E28899A8C814" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_42387D16848A88606968E28899A8123F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_44174983EBC4CA2E678CE28899A76D77" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_42387D16848A88606968E28899A8123F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_4E82B602C17C9B54EF9CE28899A88616_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_42387D16848A88606968E28899A8123F" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_4E82B602C17C9B54EF9CE28899A88616_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_4E82B602C17C9B54EF9CE28899A88616" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_42387D16848A88606968E28899A8123F" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_4E82B602C17C9B54EF9CE28899A88616" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_C23ADAF8966EC2FDC8B7E28899A895E4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_4E82B602C17C9B54EF9CE28899A88616" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_C23ADAF8966EC2FDC8B7E28899A895E4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_1215C4913554435C8FEBE28899A80990" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_4E82B602C17C9B54EF9CE28899A88616" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_1215C4913554435C8FEBE28899A80990" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_A36C5DF2152FA6B53D70E28899A84F2E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_44174983EBC4CA2E678CE28899A76D77" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_A36C5DF2152FA6B53D70E28899A84F2E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_A36C5DF2152FA6B53D70E28899A84F2E" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_A36C5DF2152FA6B53D70E28899A84F2E" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesCConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesCConvertiblePreferredStockMember_26225B8E7D5466B0DDC0E28899A852BB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E" xlink:to="loc_rubi_SeriesCConvertiblePreferredStockMember_26225B8E7D5466B0DDC0E28899A852BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_9EB44C2A4ECE95F616F5E28899A89117" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_9EB44C2A4ECE95F616F5E28899A89117" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_31F5DD40151594BFD66BE28899A887B4" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_5A6F0D50E13134FF407DE28899A8D11E" xlink:to="loc_us-gaap_CommonStockMember_31F5DD40151594BFD66BE28899A887B4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5F46906A89E7D533479AE28899A9F361" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_44174983EBC4CA2E678CE28899A76D77" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5F46906A89E7D533479AE28899A9F361" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_EE27F8E7FBF688572870E28899A932B1_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5F46906A89E7D533479AE28899A9F361" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_EE27F8E7FBF688572870E28899A932B1_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_EE27F8E7FBF688572870E28899A932B1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5F46906A89E7D533479AE28899A9F361" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_EE27F8E7FBF688572870E28899A932B1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_664AEEBC34CB576ADD12E28899A906E0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_EE27F8E7FBF688572870E28899A932B1" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_664AEEBC34CB576ADD12E28899A906E0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_E644448DAD6A55F6C180E28899A9381C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_E644448DAD6A55F6C180E28899A9381C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_98F5BC646648CAF52B49E28899A9E4E7" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_98F5BC646648CAF52B49E28899A9E4E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AssetImpairmentCharges" xlink:label="loc_us-gaap_AssetImpairmentCharges_98F546B7BBF420D99A35E28899A95AAF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_AssetImpairmentCharges_98F546B7BBF420D99A35E28899A95AAF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_B371485C1A5A6AAAAB5EE28899A99B5B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_B371485C1A5A6AAAAB5EE28899A99B5B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_7B18DB9D45B06AF49EEBE28899A9CAE4" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_7B18DB9D45B06AF49EEBE28899A9CAE4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_B8454FA14C10A19C73ACE28D129019A4" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_B8454FA14C10A19C73ACE28D129019A4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_18C624E9E342BD4A7FB2E28899AA58E7" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_18C624E9E342BD4A7FB2E28899AA58E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaap_SharePrice_D47809A040DC3B928DBBE28899AA3039" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_SharePrice_D47809A040DC3B928DBBE28899AA3039" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_930218CFE1B62A80E81FE28899AA5D8F" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_930218CFE1B62A80E81FE28899AA5D8F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAdjustmentOfWarrants" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_F36C5002BDFFA54595AEE28899AA1797" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_C65161FE147C6C9E2029E28899A987B3" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_F36C5002BDFFA54595AEE28899AA1797" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/FairValueMeasurementsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/FairValueMeasurementsWeightedAverageAssumptionsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_61B6B4F8534F44C93658C6D9E663761E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_61B6B4F8534F44C93658C6D9E663761E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_DEE0A737B6A43336B886C6D9E6638F6B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_61B6B4F8534F44C93658C6D9E663761E" xlink:to="loc_us-gaap_StatementClassOfStockAxis_DEE0A737B6A43336B886C6D9E6638F6B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_F4E4F444DF80DE5F03FBC6D9E6631212_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_DEE0A737B6A43336B886C6D9E6638F6B" xlink:to="loc_us-gaap_ClassOfStockDomain_F4E4F444DF80DE5F03FBC6D9E6631212_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_F4E4F444DF80DE5F03FBC6D9E6631212" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_DEE0A737B6A43336B886C6D9E6638F6B" xlink:to="loc_us-gaap_ClassOfStockDomain_F4E4F444DF80DE5F03FBC6D9E6631212" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesBConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesBConvertiblePreferredStockMember_12F4DDA2FE23DA23C5B6C6D9E664FA37" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_F4E4F444DF80DE5F03FBC6D9E6631212" xlink:to="loc_rubi_SeriesBConvertiblePreferredStockMember_12F4DDA2FE23DA23C5B6C6D9E664FA37" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SeriesCConvertiblePreferredStockMember" xlink:label="loc_rubi_SeriesCConvertiblePreferredStockMember_E5A27820888AFD330290C6D9E664506E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_F4E4F444DF80DE5F03FBC6D9E6631212" xlink:to="loc_rubi_SeriesCConvertiblePreferredStockMember_E5A27820888AFD330290C6D9E664506E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_FairValueAssumptionsRiskFreeInterestRate_ED7DFBFCB5FD112A6831C6D9E66411F2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:to="loc_us-gaap_FairValueAssumptionsRiskFreeInterestRate_ED7DFBFCB5FD112A6831C6D9E66411F2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssumptionsExpectedTerm" xlink:label="loc_us-gaap_FairValueAssumptionsExpectedTerm_860A24EB9D85A9767A18C6D9E6640F05" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:to="loc_us-gaap_FairValueAssumptionsExpectedTerm_860A24EB9D85A9767A18C6D9E6640F05" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_FairValueAssumptionsExpectedDividendRate_4858C49B68340CC093FDC6D9E664E585" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:to="loc_us-gaap_FairValueAssumptionsExpectedDividendRate_4858C49B68340CC093FDC6D9E664E585" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_FairValueAssumptionsExpectedVolatilityRate_75F35B3C75EAF11F9216C6D9E6640B60" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:to="loc_us-gaap_FairValueAssumptionsExpectedVolatilityRate_75F35B3C75EAF11F9216C6D9E6640B60" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ConvertiblePreferredStockWarrantsFairValueDisclosure" xlink:label="loc_rubi_ConvertiblePreferredStockWarrantsFairValueDisclosure_84BF0B31F013AC7378A4C6D9E6648876" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_B194FC38F422CF94F3F7C6D9E66419A4" xlink:to="loc_rubi_ConvertiblePreferredStockWarrantsFairValueDisclosure_84BF0B31F013AC7378A4C6D9E6648876" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GeographicInformation" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GeographicInformationDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_2B9A9B5EAD235992C485572951E86B32" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_A2AD743DD927A4DA9394572951E8FA3D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_2B9A9B5EAD235992C485572951E86B32" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_A2AD743DD927A4DA9394572951E8FA3D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_B7E8EA4B8FFA15A254FA572951E8F5EF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_A2AD743DD927A4DA9394572951E8FA3D" xlink:to="loc_us-gaap_StatementGeographicalAxis_B7E8EA4B8FFA15A254FA572951E8F5EF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_B7E8EA4B8FFA15A254FA572951E8F5EF" xlink:to="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_B7E8EA4B8FFA15A254FA572951E8F5EF" xlink:to="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/country/2013/country-2013-01-31.xsd#country_US" xlink:label="loc_country_US_885804D6872A163E2110572951E8C518" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA" xlink:to="loc_country_US_885804D6872A163E2110572951E8C518" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/country/2013/country-2013-01-31.xsd#country_DE" xlink:label="loc_country_DE_5D00A9B92BBFF0C3FB47577EB6185432" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA" xlink:to="loc_country_DE_5D00A9B92BBFF0C3FB47577EB6185432" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/country/2013/country-2013-01-31.xsd#country_NL" xlink:label="loc_country_NL_1442F486B12B593ADC22572951E83A49" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA" xlink:to="loc_country_NL_1442F486B12B593ADC22572951E83A49" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_OtherInternationalMember" xlink:label="loc_rubi_OtherInternationalMember_C595763E5972E2D8E888572951E80B7E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_9276BC8ACA95227524F2572951E8B3CA" xlink:to="loc_rubi_OtherInternationalMember_C595763E5972E2D8E888572951E80B7E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_193054B3BDE602D833E3572951E88828" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_2B9A9B5EAD235992C485572951E86B32" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_193054B3BDE602D833E3572951E88828" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GeographicInformationTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssets" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6BB24403065BA132F4F999D8E35AA57C" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1318298ACA423B17BCD99D8E3593326" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6BB24403065BA132F4F999D8E35AA57C" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1318298ACA423B17BCD99D8E3593326" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DC155402CD38FB3BD0A299D8E359C093" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1318298ACA423B17BCD99D8E3593326" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DC155402CD38FB3BD0A299D8E359C093" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DC155402CD38FB3BD0A299D8E359C093" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_DC155402CD38FB3BD0A299D8E359C093" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_029DD81E72196486665099D8E35A790E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_029DD81E72196486665099D8E35A790E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_66AD2F66A96E0E0CC08399D8E35A6C5F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_66AD2F66A96E0E0CC08399D8E35A6C5F" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_CustomerRelationshipsandOtherIntangibleAssetsMember" xlink:label="loc_rubi_CustomerRelationshipsandOtherIntangibleAssetsMember_9E652C73B8B503333FE999D8E35A6B78" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94D7DBE4BA736F615C3399D8E359A433" xlink:to="loc_rubi_CustomerRelationshipsandOtherIntangibleAssetsMember_9E652C73B8B503333FE999D8E35A6B78" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_740976BD2CE04A2AA74199D8E35ACEA4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6BB24403065BA132F4F999D8E35AA57C" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_740976BD2CE04A2AA74199D8E35ACEA4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_A7B80DE1DDB6189C785399D8E35AE0D5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6BB24403065BA132F4F999D8E35AA57C" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_A7B80DE1DDB6189C785399D8E35AE0D5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_871C1116F8AE41905E3B99D8E35AC3CE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6BB24403065BA132F4F999D8E35AA57C" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_871C1116F8AE41905E3B99D8E35AC3CE" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsFiniteLivedIntangibleAssetsFutureAmortizationExpenseDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsGoodwillDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_GoodwillLineItems" xlink:label="loc_us-gaap_GoodwillLineItems_993A1319B420FC590002BA2AF303BA8A" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfGoodwillTable" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_B1DF6BEAE18323253783BA2AF30209A1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_993A1319B420FC590002BA2AF303BA8A" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_B1DF6BEAE18323253783BA2AF30209A1" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_E26B8BFA14A9F9B56059BA2AF302CCEB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_B1DF6BEAE18323253783BA2AF30209A1" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_E26B8BFA14A9F9B56059BA2AF302CCEB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_E26B8BFA14A9F9B56059BA2AF302CCEB" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_E26B8BFA14A9F9B56059BA2AF302CCEB" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ISocketIncMember" xlink:label="loc_rubi_ISocketIncMember_0B97389F395F17099351BA2AF302EF96" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA" xlink:to="loc_rubi_ISocketIncMember_0B97389F395F17099351BA2AF302EF96" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ShinyIncMember" xlink:label="loc_rubi_ShinyIncMember_8778C2867C312E727BAEBA2AF3023568" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA" xlink:to="loc_rubi_ShinyIncMember_8778C2867C312E727BAEBA2AF3023568" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_MobSmithMember" xlink:label="loc_rubi_MobSmithMember_4738E48766C9BB7B7FC6BA4B71AEC32E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8C085EB1F93B0DBD463BBA2AF3021BCA" xlink:to="loc_rubi_MobSmithMember_4738E48766C9BB7B7FC6BA4B71AEC32E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_GoodwillRollForward" xlink:label="loc_us-gaap_GoodwillRollForward_DAB31FE5B74D7690BCE3BA2AF303ABDB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_993A1319B420FC590002BA2AF303BA8A" xlink:to="loc_us-gaap_GoodwillRollForward_DAB31FE5B74D7690BCE3BA2AF303ABDB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_1F15A8AEE0B346648256BA2AF30337CE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_DAB31FE5B74D7690BCE3BA2AF303ABDB" xlink:to="loc_us-gaap_Goodwill_1F15A8AEE0B346648256BA2AF30337CE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_GoodwillAcquiredDuringPeriod" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_09F2680C066FD2D8A1E2BA2AF3036272" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_DAB31FE5B74D7690BCE3BA2AF303ABDB" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_09F2680C066FD2D8A1E2BA2AF3036272" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsNarrativeDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/GoodwillAndIntangibleAssetsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxes" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseBenefitDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesIncomeBeforeIncomeTaxDomesticAndForeignDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TaxCreditCarryforwardLineItems" xlink:label="loc_us-gaap_TaxCreditCarryforwardLineItems_3325C708E46A39A48203D7B01454965D" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TaxCreditCarryforwardTable" xlink:label="loc_us-gaap_TaxCreditCarryforwardTable_2919A07D99CDD1B8348FD7B0145257CB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_3325C708E46A39A48203D7B01454965D" xlink:to="loc_us-gaap_TaxCreditCarryforwardTable_2919A07D99CDD1B8348FD7B0145257CB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_FD10DE939E3D5DA295BDD7B01453B8FA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TaxCreditCarryforwardTable_2919A07D99CDD1B8348FD7B0145257CB" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_FD10DE939E3D5DA295BDD7B01453B8FA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_4C4FE083E2BCBAA5CF72D7B01453B04E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_FD10DE939E3D5DA295BDD7B01453B8FA" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_4C4FE083E2BCBAA5CF72D7B01453B04E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_4C4FE083E2BCBAA5CF72D7B01453B04E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_FD10DE939E3D5DA295BDD7B01453B8FA" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_4C4FE083E2BCBAA5CF72D7B01453B04E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ResearchMember" xlink:label="loc_us-gaap_ResearchMember_0DCA2B18C8D31FE3D2D8D7B01453A8B0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_4C4FE083E2BCBAA5CF72D7B01453B04E" xlink:to="loc_us-gaap_ResearchMember_0DCA2B18C8D31FE3D2D8D7B01453A8B0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_E75768F9F5FE35401FADD7B014538C9D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TaxCreditCarryforwardTable_2919A07D99CDD1B8348FD7B0145257CB" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_E75768F9F5FE35401FADD7B014538C9D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_2B6EDED41251904C0606D7B014539BBF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_E75768F9F5FE35401FADD7B014538C9D" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_2B6EDED41251904C0606D7B014539BBF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_2B6EDED41251904C0606D7B014539BBF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_E75768F9F5FE35401FADD7B014538C9D" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_2B6EDED41251904C0606D7B014539BBF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DomesticCountryMember" xlink:label="loc_us-gaap_DomesticCountryMember_BAF1973BD8948021344FD7B01453BD9C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_2B6EDED41251904C0606D7B014539BBF" xlink:to="loc_us-gaap_DomesticCountryMember_BAF1973BD8948021344FD7B01453BD9C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_F9245D9003E0ADEC7E50D7B0145475F5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_2B6EDED41251904C0606D7B014539BBF" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_F9245D9003E0ADEC7E50D7B0145475F5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_54460692AAC2C58E417FD7B014543246" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_3325C708E46A39A48203D7B01454965D" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_54460692AAC2C58E417FD7B014543246" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_F242EED3FD9EEA95D728D7B0145905C5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_3325C708E46A39A48203D7B01454965D" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_F242EED3FD9EEA95D728D7B0145905C5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OperatingLossCarryforwardsLineItems" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_3EDC8F8F3DA9515DEC41D7B0145A5053" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OperatingLossCarryforwardsTable" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_E0171254CD8380CEEE44D7B01459DC1E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_3EDC8F8F3DA9515DEC41D7B0145A5053" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_E0171254CD8380CEEE44D7B01459DC1E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_91E149706BEA3EC3CC4CD7B01459C81B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_E0171254CD8380CEEE44D7B01459DC1E" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_91E149706BEA3EC3CC4CD7B01459C81B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_AC9058C3DB36E8BBDF9CD7B0145AC38C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_E0171254CD8380CEEE44D7B01459DC1E" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_AC9058C3DB36E8BBDF9CD7B0145AC38C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9A58E99EAB4EA89E6CABD7B0145A330B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_AC9058C3DB36E8BBDF9CD7B0145AC38C" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9A58E99EAB4EA89E6CABD7B0145A330B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9A58E99EAB4EA89E6CABD7B0145A330B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_AC9058C3DB36E8BBDF9CD7B0145AC38C" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9A58E99EAB4EA89E6CABD7B0145A330B" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_ISocketIncMember" xlink:label="loc_rubi_ISocketIncMember_72EF13B48CCB3FF4FBE2D7B0145AD49C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9A58E99EAB4EA89E6CABD7B0145A330B" xlink:to="loc_rubi_ISocketIncMember_72EF13B48CCB3FF4FBE2D7B0145AD49C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="loc_us-gaap_OperatingLossCarryforwards_F66B80C1AFB32F9D4018D7B0145AB6D7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_3EDC8F8F3DA9515DEC41D7B0145A5053" xlink:to="loc_us-gaap_OperatingLossCarryforwards_F66B80C1AFB32F9D4018D7B0145AB6D7" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/IncomeTaxesUnrecognizedTaxBenefitsDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCosts" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCostsDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCostsNarrativeDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/InternalUseSoftwareDevelopmentCostsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NatureOfOperations" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NatureOfOperationsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_407D751DE42EACA27B8699D8E3D55DFF" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_41CF610CB68F3D188E7E99D8E3D4699E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_407D751DE42EACA27B8699D8E3D55DFF" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_41CF610CB68F3D188E7E99D8E3D4699E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_54E07D0B594751B9CAD699D8E3D5B26E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_41CF610CB68F3D188E7E99D8E3D4699E" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_54E07D0B594751B9CAD699D8E3D5B26E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_4C5995737A181D17769E99D8E3D5996A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_54E07D0B594751B9CAD699D8E3D5B26E" xlink:to="loc_us-gaap_EquityComponentDomain_4C5995737A181D17769E99D8E3D5996A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_4C5995737A181D17769E99D8E3D5996A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_54E07D0B594751B9CAD699D8E3D5B26E" xlink:to="loc_us-gaap_EquityComponentDomain_4C5995737A181D17769E99D8E3D5996A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_E270C1D0D2806AB0F25999D8E3D5D967" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_4C5995737A181D17769E99D8E3D5996A" xlink:to="loc_us-gaap_CommonStockMember_E270C1D0D2806AB0F25999D8E3D5D967" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_741CC86530440EA962F899D8E3D58CC6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_407D751DE42EACA27B8699D8E3D55DFF" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_741CC86530440EA962F899D8E3D58CC6" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_InitialPublicOfferingSharesSoldbyExistingStockholders" xlink:label="loc_rubi_InitialPublicOfferingSharesSoldbyExistingStockholders_F6F29F4938B73AFC8C3F99D8E3D53F20" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_407D751DE42EACA27B8699D8E3D55DFF" xlink:to="loc_rubi_InitialPublicOfferingSharesSoldbyExistingStockholders_F6F29F4938B73AFC8C3F99D8E3D53F20" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholders" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersAntiDilutiveDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_E473AE3A89E72483E7CBCCB55B130BC3" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_1DD5C62A58C9D9709B0BCCB55B11CEE5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_E473AE3A89E72483E7CBCCB55B130BC3" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_1DD5C62A58C9D9709B0BCCB55B11CEE5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_63B8D483E8931A448D3BCCB55B127FBC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_1DD5C62A58C9D9709B0BCCB55B11CEE5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_63B8D483E8931A448D3BCCB55B127FBC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_63B8D483E8931A448D3BCCB55B127FBC" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_63B8D483E8931A448D3BCCB55B127FBC" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockOptionMember" xlink:label="loc_us-gaap_StockOptionMember_86D2420D3C5427F48597CCB55B128946" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:to="loc_us-gaap_StockOptionMember_86D2420D3C5427F48597CCB55B128946" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_071778D1E101F35EBB59CCB55B12D3C6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:to="loc_us-gaap_RestrictedStockMember_071778D1E101F35EBB59CCB55B12D3C6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_93F8F53D4FD2D66ADD55CCB55B12A827" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_93F8F53D4FD2D66ADD55CCB55B12A827" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SharesHeldinEscrowMember" xlink:label="loc_rubi_SharesHeldinEscrowMember_A6075682C2E2C38F5EE5CCB55B13B21B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:to="loc_rubi_SharesHeldinEscrowMember_A6075682C2E2C38F5EE5CCB55B13B21B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_1D266C02E39412BF5E2CCCB55B135198" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_1D266C02E39412BF5E2CCCB55B135198" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_WarrantMember" xlink:label="loc_us-gaap_WarrantMember_B3AD032CF205E294052CCCB55B1361E7" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9FE85F3F1B04E5766D21CCB55B1288BF" xlink:to="loc_us-gaap_WarrantMember_B3AD032CF205E294052CCCB55B1361E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_6CCBA124FA470C0FDE7BCCB55B13030F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_E473AE3A89E72483E7CBCCB55B130BC3" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_6CCBA124FA470C0FDE7BCCB55B13030F" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersNarrativeDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/NetLossPerShareAttributableToCommonStockholdersTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/PropertyAndEquipment" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/PropertyAndEquipmentDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_21D2C3F7BE5D853556C1168FACCF81A0" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_F166A1B3D7C7E72A82B4168FACCF0F4F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_21D2C3F7BE5D853556C1168FACCF81A0" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_F166A1B3D7C7E72A82B4168FACCF0F4F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_FF0CB30719F3E4F60CCE168FACCFA05C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_F166A1B3D7C7E72A82B4168FACCF0F4F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_FF0CB30719F3E4F60CCE168FACCFA05C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_FF0CB30719F3E4F60CCE168FACCFA05C" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_FF0CB30719F3E4F60CCE168FACCFA05C" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_444890F920C5D0B1432517901508637B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_444890F920C5D0B1432517901508637B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaap_ComputerEquipmentMember_9BE611BA8DA20E441AFB168FACCF7426" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3" xlink:to="loc_us-gaap_ComputerEquipmentMember_9BE611BA8DA20E441AFB168FACCF7426" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_3A16B9C135795F23175B17AE9F2E5143" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_3A16B9C135795F23175B17AE9F2E5143" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_E3092183B18B2442959E168FACCF967E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A0AE3717F663CFDB0201168FACCFB1A3" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_E3092183B18B2442959E168FACCF967E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_CA664C17C51244197907168FACCF5C65" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_21D2C3F7BE5D853556C1168FACCF81A0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_CA664C17C51244197907168FACCF5C65" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_390BAC114A338CC8B49D168FACD03207" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_21D2C3F7BE5D853556C1168FACCF81A0" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_390BAC114A338CC8B49D168FACD03207" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_7E03D65CCDD73D0B6107168FACD01009" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_21D2C3F7BE5D853556C1168FACCF81A0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_7E03D65CCDD73D0B6107168FACD01009" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/PropertyAndEquipmentNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_76E08017CDA67C78FFC3D77228E91B61" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_320775C37DF7267F1322D77228E9317E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_76E08017CDA67C78FFC3D77228E91B61" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_320775C37DF7267F1322D77228E9317E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_F3C02881AC03114BE02CD77228E94035" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_320775C37DF7267F1322D77228E9317E" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_F3C02881AC03114BE02CD77228E94035" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2818BA750FD9C5E8A5CCD77228E920A5_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_F3C02881AC03114BE02CD77228E94035" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2818BA750FD9C5E8A5CCD77228E920A5_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2818BA750FD9C5E8A5CCD77228E920A5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_F3C02881AC03114BE02CD77228E94035" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2818BA750FD9C5E8A5CCD77228E920A5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AssetsHeldUnderCapitalLeasesMember" xlink:label="loc_us-gaap_AssetsHeldUnderCapitalLeasesMember_3B52CF5C5D85802129F8D77228E91E9C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_2818BA750FD9C5E8A5CCD77228E920A5" xlink:to="loc_us-gaap_AssetsHeldUnderCapitalLeasesMember_3B52CF5C5D85802129F8D77228E91E9C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_DF2F61438857BE609C70D77228E91586" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_320775C37DF7267F1322D77228E9317E" xlink:to="loc_us-gaap_RangeAxis_DF2F61438857BE609C70D77228E91586" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_29A55619634D28AA510ED77228E99746_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_DF2F61438857BE609C70D77228E91586" xlink:to="loc_us-gaap_RangeMember_29A55619634D28AA510ED77228E99746_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_29A55619634D28AA510ED77228E99746" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_DF2F61438857BE609C70D77228E91586" xlink:to="loc_us-gaap_RangeMember_29A55619634D28AA510ED77228E99746" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_1F16925A3D701DA424E0D77228E9F004" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_76E08017CDA67C78FFC3D77228E91B61" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_1F16925A3D701DA424E0D77228E9F004" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_B6340BFCF2D798DA79B7D77228E96FBF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_76E08017CDA67C78FFC3D77228E91B61" xlink:to="loc_us-gaap_Depreciation_B6340BFCF2D798DA79B7D77228E96FBF" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/PropertyAndEquipmentTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/RelatedPartyTransactions" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5E21F6FDB31EC169618FBBEA46D2C1DA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5E21F6FDB31EC169618FBBEA46D2C1DA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_93EB1834746047888433BBEA46D242D2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5E21F6FDB31EC169618FBBEA46D2C1DA" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_93EB1834746047888433BBEA46D242D2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_764EF1F7BD1EDC87C82FBBEA46D2BF5F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_93EB1834746047888433BBEA46D242D2" xlink:to="loc_us-gaap_RelatedPartyDomain_764EF1F7BD1EDC87C82FBBEA46D2BF5F_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_764EF1F7BD1EDC87C82FBBEA46D2BF5F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_93EB1834746047888433BBEA46D242D2" xlink:to="loc_us-gaap_RelatedPartyDomain_764EF1F7BD1EDC87C82FBBEA46D2BF5F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AffiliatedEntityMember" xlink:label="loc_us-gaap_AffiliatedEntityMember_56F92269ED5AE91A55B4BBEA46D2A572" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_764EF1F7BD1EDC87C82FBBEA46D2BF5F" xlink:to="loc_us-gaap_AffiliatedEntityMember_56F92269ED5AE91A55B4BBEA46D2A572" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_CBBC47742B2999CCC909BBEA46D20EFD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5E21F6FDB31EC169618FBBEA46D2C1DA" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_CBBC47742B2999CCC909BBEA46D20EFD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_AB4402CB5FF6E4500693BBEA46D3633B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_CBBC47742B2999CCC909BBEA46D20EFD" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_AB4402CB5FF6E4500693BBEA46D3633B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_AB4402CB5FF6E4500693BBEA46D3633B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_CBBC47742B2999CCC909BBEA46D20EFD" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_AB4402CB5FF6E4500693BBEA46D3633B" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SubleaseWithRelatedPartyMember" xlink:label="loc_rubi_SubleaseWithRelatedPartyMember_14564B95B2A24D982B37BBEA46D3C7AC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_AB4402CB5FF6E4500693BBEA46D3633B" xlink:to="loc_rubi_SubleaseWithRelatedPartyMember_14564B95B2A24D982B37BBEA46D3C7AC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RevenueFromRelatedParties" xlink:label="loc_us-gaap_RevenueFromRelatedParties_24DCB5E20F1FC56D3E4FBBEA46D3A5A3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:to="loc_us-gaap_RevenueFromRelatedParties_24DCB5E20F1FC56D3E4FBBEA46D3A5A3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccountsPayableRelatedPartiesCurrentAndNoncurrent" xlink:label="loc_us-gaap_AccountsPayableRelatedPartiesCurrentAndNoncurrent_001BAD444712977AF344BBEA46D36BD7" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:to="loc_us-gaap_AccountsPayableRelatedPartiesCurrentAndNoncurrent_001BAD444712977AF344BBEA46D36BD7" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_LesseeLeasingArrangementsOperatingLeasesTerminationNoticeTerm" xlink:label="loc_rubi_LesseeLeasingArrangementsOperatingLeasesTerminationNoticeTerm_1F45E1ADC7064856FF60BBEA46D3D7E0" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:to="loc_rubi_LesseeLeasingArrangementsOperatingLeasesTerminationNoticeTerm_1F45E1ADC7064856FF60BBEA46D3D7E0" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_LesseeLeasingArrangementsOperatingLeasesEarlyTerminationFee" xlink:label="loc_rubi_LesseeLeasingArrangementsOperatingLeasesEarlyTerminationFee_121DF782BCA8F61C9F41BBEA46D381B2" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:to="loc_rubi_LesseeLeasingArrangementsOperatingLeasesEarlyTerminationFee_121DF782BCA8F61C9F41BBEA46D381B2" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_LesseeLeasingArrangementsOperatingLeasesEarlyTerminationTenantImprovementAllowanceThresholdMaximumBeforePenalty" xlink:label="loc_rubi_LesseeLeasingArrangementsOperatingLeasesEarlyTerminationTenantImprovementAllowanceThresholdMaximumBeforePenalty_F51A1F80ACAE34AAF4A7BBEA46D3800D" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_E8FA32428148BC765E0EBBEA46D36ADC" xlink:to="loc_rubi_LesseeLeasingArrangementsOperatingLeasesEarlyTerminationTenantImprovementAllowanceThresholdMaximumBeforePenalty_F51A1F80ACAE34AAF4A7BBEA46D3800D" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensation" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C42A1DC01BB0477E7EBCC6D9E5DD95E0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C42A1DC01BB0477E7EBCC6D9E5DD95E0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_627E069039917ADE4279C6D9E5DD3F7A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C42A1DC01BB0477E7EBCC6D9E5DD95E0" xlink:to="loc_us-gaap_PlanNameAxis_627E069039917ADE4279C6D9E5DD3F7A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_888C3484D89DD1F2E8BAC6D9E5DDA910_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_627E069039917ADE4279C6D9E5DD3F7A" xlink:to="loc_us-gaap_PlanNameDomain_888C3484D89DD1F2E8BAC6D9E5DDA910_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_888C3484D89DD1F2E8BAC6D9E5DDA910" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_627E069039917ADE4279C6D9E5DD3F7A" xlink:to="loc_us-gaap_PlanNameDomain_888C3484D89DD1F2E8BAC6D9E5DDA910" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_A2014EquityIncentivePlanMember" xlink:label="loc_rubi_A2014EquityIncentivePlanMember_6B3E3E4D60ED788A9DA2C6D9E5DE3AA6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_888C3484D89DD1F2E8BAC6D9E5DDA910" xlink:to="loc_rubi_A2014EquityIncentivePlanMember_6B3E3E4D60ED788A9DA2C6D9E5DE3AA6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_76F8EA275B5D6B0776C4C6D9E5DE79A3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_76F8EA275B5D6B0776C4C6D9E5DE79A3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_174DE22FBFD3C4888A0EC6D9E5DEC492" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_174DE22FBFD3C4888A0EC6D9E5DEC492" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_BEC47BAF2755E0A258CEC6D9E5DE7CB0" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_BEC47BAF2755E0A258CEC6D9E5DE7CB0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_5C11E18B1A0537BF39CCC6D9E5DEA351" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_5C11E18B1A0537BF39CCC6D9E5DEA351" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_EvergreenAnnualIncrease" xlink:label="loc_rubi_EvergreenAnnualIncrease_D06706EAA8EA38C8B6DFC6D9E5DEB072" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8D571850A58FB21AB465C6D9E5DE0DFD" xlink:to="loc_rubi_EvergreenAnnualIncrease_D06706EAA8EA38C8B6DFC6D9E5DEB072" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationEmployeeStockPurchasePlanDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F9F24A26F843DF23808FBBEA4765FB91" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F9F24A26F843DF23808FBBEA4765FB91" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_F0F38BD4C9A363818819BBEA47656E6E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F9F24A26F843DF23808FBBEA4765FB91" xlink:to="loc_us-gaap_PlanNameAxis_F0F38BD4C9A363818819BBEA47656E6E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_88CE4445E797EBF33EBDBBEA4765825C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_F0F38BD4C9A363818819BBEA47656E6E" xlink:to="loc_us-gaap_PlanNameDomain_88CE4445E797EBF33EBDBBEA4765825C_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_88CE4445E797EBF33EBDBBEA4765825C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_F0F38BD4C9A363818819BBEA47656E6E" xlink:to="loc_us-gaap_PlanNameDomain_88CE4445E797EBF33EBDBBEA4765825C" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_A2014EmployeeStockPurchasePlanMember" xlink:label="loc_rubi_A2014EmployeeStockPurchasePlanMember_CF90D52DE12DDB04E2C1BBEA47652C15" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_88CE4445E797EBF33EBDBBEA4765825C" xlink:to="loc_rubi_A2014EmployeeStockPurchasePlanMember_CF90D52DE12DDB04E2C1BBEA47652C15" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_67650F8DBC76B8920D5FBBEA47669464" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F9F24A26F843DF23808FBBEA4765FB91" xlink:to="loc_us-gaap_AwardTypeAxis_67650F8DBC76B8920D5FBBEA47669464" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_111577B75E692D1626A0BBEA4766E7EB_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_67650F8DBC76B8920D5FBBEA47669464" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_111577B75E692D1626A0BBEA4766E7EB_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_111577B75E692D1626A0BBEA4766E7EB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_67650F8DBC76B8920D5FBBEA47669464" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_111577B75E692D1626A0BBEA4766E7EB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_0D0517718FB9CD85E935BBEA47664907" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_111577B75E692D1626A0BBEA4766E7EB" xlink:to="loc_us-gaap_EmployeeStockMember_0D0517718FB9CD85E935BBEA47664907" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_B8C32439993D7F04A8AABBEA476696BF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_B8C32439993D7F04A8AABBEA476696BF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_4394D65CBD2202FAE77CBBEA476622BB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_4394D65CBD2202FAE77CBBEA476622BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_BEEDAC44A496C4ECFF29BBEA47667980" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_BEEDAC44A496C4ECFF29BBEA47667980" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SharebasedCompensationArrangementbySharebasedPaymentAwardIncreaseinSharesAuthorizedPercentofOutstandingStock" xlink:label="loc_rubi_SharebasedCompensationArrangementbySharebasedPaymentAwardIncreaseinSharesAuthorizedPercentofOutstandingStock_DDF2B83E2125732926CDBBEA47669358" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:to="loc_rubi_SharebasedCompensationArrangementbySharebasedPaymentAwardIncreaseinSharesAuthorizedPercentofOutstandingStock_DDF2B83E2125732926CDBBEA47669358" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_FBA2CC3D6803497C4096BBEA4766E4DF" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E25BBFAC1953BE94D8C2BBEA4766F062" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_FBA2CC3D6803497C4096BBEA4766E4DF" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationExpenseDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_7C6A604BE8B60A208E6930A711766FA9" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_1AEE0775FED7FDE7C9CD30A71175073F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_7C6A604BE8B60A208E6930A711766FA9" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_1AEE0775FED7FDE7C9CD30A71175073F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_05CBF2B670774AD8982230A711750C1F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_1AEE0775FED7FDE7C9CD30A71175073F" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_05CBF2B670774AD8982230A711750C1F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_05CBF2B670774AD8982230A711750C1F" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_05CBF2B670774AD8982230A711750C1F" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaap_CostOfSalesMember_28B4A5C3871DE4E149A530A71175305B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4" xlink:to="loc_us-gaap_CostOfSalesMember_28B4A5C3871DE4E149A530A71175305B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_5B629A72842FBBD220FC30A711759CAD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_5B629A72842FBBD220FC30A711759CAD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_C3D481394429BCA9B41930A71175DC27" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_C3D481394429BCA9B41930A71175DC27" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_E3B29A8E569C86BC4E9330A71175C9EC" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C459762ABB64541E4BAC30A71175E0D4" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_E3B29A8E569C86BC4E9330A71175C9EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_63791D040E712260C2F430A711764004" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_7C6A604BE8B60A208E6930A711766FA9" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_63791D040E712260C2F430A711764004" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockActivityDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_287885B7622B5886F439C6D9E5C85C08" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8CA59FE734CE6F4BB9FEC6D9E5C8F9A4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_287885B7622B5886F439C6D9E5C85C08" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8CA59FE734CE6F4BB9FEC6D9E5C8F9A4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_378344E76CA9D7CCCC8DC6D9E5C8B05D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8CA59FE734CE6F4BB9FEC6D9E5C8F9A4" xlink:to="loc_us-gaap_AwardTypeAxis_378344E76CA9D7CCCC8DC6D9E5C8B05D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_C067B1DA00940E9E7BF7C6D9E5C81F9E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_378344E76CA9D7CCCC8DC6D9E5C8B05D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_C067B1DA00940E9E7BF7C6D9E5C81F9E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_C067B1DA00940E9E7BF7C6D9E5C81F9E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_378344E76CA9D7CCCC8DC6D9E5C8B05D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_C067B1DA00940E9E7BF7C6D9E5C81F9E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_288AB7C80E9A4994D60AC6D9E5C81A51" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_C067B1DA00940E9E7BF7C6D9E5C81F9E" xlink:to="loc_us-gaap_RestrictedStockMember_288AB7C80E9A4994D60AC6D9E5C81A51" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_D68FC85EE86B1F499D99C6D9E5C88050" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_287885B7622B5886F439C6D9E5C85C08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_D68FC85EE86B1F499D99C6D9E5C88050" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_162813DF368F177A64FAC7005558A711" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_287885B7622B5886F439C6D9E5C85C08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_162813DF368F177A64FAC7005558A711" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_AE60CE3358BEE73A5482C6D9E5C80E6C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_287885B7622B5886F439C6D9E5C85C08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_AE60CE3358BEE73A5482C6D9E5C80E6C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_2A88906BCAAA5DC2E31AC6D9E5C8AEA1" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_287885B7622B5886F439C6D9E5C85C08" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_2A88906BCAAA5DC2E31AC6D9E5C8AEA1" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D366BAC6D68200B3FEB6C6D9E5C2B22B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D366BAC6D68200B3FEB6C6D9E5C2B22B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_C41466DA903C7437BA81C6D9E5C290FD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D366BAC6D68200B3FEB6C6D9E5C2B22B" xlink:to="loc_us-gaap_AwardTypeAxis_C41466DA903C7437BA81C6D9E5C290FD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_51DCF62F5AD545CE89A5C6D9E5C25EE5_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_C41466DA903C7437BA81C6D9E5C290FD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_51DCF62F5AD545CE89A5C6D9E5C25EE5_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_51DCF62F5AD545CE89A5C6D9E5C25EE5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_C41466DA903C7437BA81C6D9E5C290FD" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_51DCF62F5AD545CE89A5C6D9E5C25EE5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_EFB5A65A08135E5BA2B8C6D9E5C3139E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_51DCF62F5AD545CE89A5C6D9E5C25EE5" xlink:to="loc_us-gaap_RestrictedStockMember_EFB5A65A08135E5BA2B8C6D9E5C3139E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_1FCBE9209D876F9D259FC6D9E5C376FF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D366BAC6D68200B3FEB6C6D9E5C2B22B" xlink:to="loc_us-gaap_TitleOfIndividualAxis_1FCBE9209D876F9D259FC6D9E5C376FF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_BD9003EF28A187D63DACC6D9E5C3623C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_1FCBE9209D876F9D259FC6D9E5C376FF" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_BD9003EF28A187D63DACC6D9E5C3623C_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_BD9003EF28A187D63DACC6D9E5C3623C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_1FCBE9209D876F9D259FC6D9E5C376FF" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_BD9003EF28A187D63DACC6D9E5C3623C" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_EmployeeandCertainExecutivesMember" xlink:label="loc_rubi_EmployeeandCertainExecutivesMember_D6736E2FFB12F437D41CC6D9E5C32A2A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_BD9003EF28A187D63DACC6D9E5C3623C" xlink:to="loc_rubi_EmployeeandCertainExecutivesMember_D6736E2FFB12F437D41CC6D9E5C32A2A" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_CertainExecutivesMember" xlink:label="loc_rubi_CertainExecutivesMember_EAD2C80E4CEE0898C1C5C6D9E5C385A2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_rubi_EmployeeandCertainExecutivesMember_D6736E2FFB12F437D41CC6D9E5C32A2A" xlink:to="loc_rubi_CertainExecutivesMember_EAD2C80E4CEE0898C1C5C6D9E5C385A2" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_NonEmployeeMember" xlink:label="loc_rubi_NonEmployeeMember_AD2CB9ECBE028432A152C6D9E5C331D9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_BD9003EF28A187D63DACC6D9E5C3623C" xlink:to="loc_rubi_NonEmployeeMember_AD2CB9ECBE028432A152C6D9E5C331D9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_17C02DF10B734365723CC6D9E5C32BB8" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D366BAC6D68200B3FEB6C6D9E5C2B22B" xlink:to="loc_us-gaap_VestingAxis_17C02DF10B734365723CC6D9E5C32BB8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_17C02DF10B734365723CC6D9E5C32BB8" xlink:to="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_17C02DF10B734365723CC6D9E5C32BB8" xlink:to="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SharebasedCompensationAwardTrancheOneMember" xlink:label="loc_rubi_SharebasedCompensationAwardTrancheOneMember_72003C41D8932B376779C6D9E5C3E882" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D" xlink:to="loc_rubi_SharebasedCompensationAwardTrancheOneMember_72003C41D8932B376779C6D9E5C3E882" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SharebasedCompensationAwardTrancheTwoMember" xlink:label="loc_rubi_SharebasedCompensationAwardTrancheTwoMember_91714FB20DEE375B6127C6D9E5C34B08" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D" xlink:to="loc_rubi_SharebasedCompensationAwardTrancheTwoMember_91714FB20DEE375B6127C6D9E5C34B08" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SharebasedCompensationAwardTrancheThreeMember" xlink:label="loc_rubi_SharebasedCompensationAwardTrancheThreeMember_A5F75CE9F03BD87032B4C6D9E5C3BBE0" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_22E6860EF113D3FBE96FC6D9E5C3DD7D" xlink:to="loc_rubi_SharebasedCompensationAwardTrancheThreeMember_A5F75CE9F03BD87032B4C6D9E5C3BBE0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_8DC1A58C675D9582E4DDC6D9E5C355DB" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D366BAC6D68200B3FEB6C6D9E5C2B22B" xlink:to="loc_us-gaap_RangeAxis_8DC1A58C675D9582E4DDC6D9E5C355DB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_90EB5B9BF7357FA189E5C6D9E5C3A864_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_8DC1A58C675D9582E4DDC6D9E5C355DB" xlink:to="loc_us-gaap_RangeMember_90EB5B9BF7357FA189E5C6D9E5C3A864_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_90EB5B9BF7357FA189E5C6D9E5C3A864" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_8DC1A58C675D9582E4DDC6D9E5C355DB" xlink:to="loc_us-gaap_RangeMember_90EB5B9BF7357FA189E5C6D9E5C3A864" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_54CBB29155AAEF50713DC6D9E5C3AAD6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_90EB5B9BF7357FA189E5C6D9E5C3A864" xlink:to="loc_us-gaap_MinimumMember_54CBB29155AAEF50713DC6D9E5C3AAD6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_67AC03996F3EBBFCD706C6D9E5C45BF8" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_90EB5B9BF7357FA189E5C6D9E5C3A864" xlink:to="loc_us-gaap_MaximumMember_67AC03996F3EBBFCD706C6D9E5C45BF8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_49767BABF63F52E9EDFDC6D9E5C46EF7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_49767BABF63F52E9EDFDC6D9E5C46EF7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2EBC6A4C044194162457C6D9E5C4DE07" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2EBC6A4C044194162457C6D9E5C4DE07" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_68BA91DBA744A4EE118FC6D9E5C414E1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_68BA91DBA744A4EE118FC6D9E5C414E1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_0A92A8FE5675911D5828C6D9E5C45DC0" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_0A92A8FE5675911D5828C6D9E5C45DC0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_707E92FFCAB592A5BF72C6D9E5C4CFA1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_707E92FFCAB592A5BF72C6D9E5C4CFA1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_25BFBDF61253B57287CFC6D9E5C45E25" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_25BFBDF61253B57287CFC6D9E5C45E25" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_3D4ED25858E9A04F107EC6D9E5C4A5DB" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_3D4ED25858E9A04F107EC6D9E5C4A5DB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_01F847B53435FF9A2AA2C6D9E5C44DAC" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_01F847B53435FF9A2AA2C6D9E5C44DAC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_E7C79963643DC307DF30C6D9E5C491EE" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_E7C79963643DC307DF30C6D9E5C491EE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_57C99200822AF0ACD874C6D9E5C45C1C" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B5D604723BE5812B2066C6D9E5C43636" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_57C99200822AF0ACD874C6D9E5C45C1C" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E1AC7153C6A6743B03C5C6D9E5BB9422" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_794D618D1F1218968C13C6D9E5BA90B7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E1AC7153C6A6743B03C5C6D9E5BB9422" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_794D618D1F1218968C13C6D9E5BA90B7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_6B6F1511775E799326EDC6D9E5BA075B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_794D618D1F1218968C13C6D9E5BA90B7" xlink:to="loc_us-gaap_AwardTypeAxis_6B6F1511775E799326EDC6D9E5BA075B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_65FB5CE1E10E52C2B83BC6D9E5BA83A4_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6B6F1511775E799326EDC6D9E5BA075B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_65FB5CE1E10E52C2B83BC6D9E5BA83A4_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_65FB5CE1E10E52C2B83BC6D9E5BA83A4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6B6F1511775E799326EDC6D9E5BA075B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_65FB5CE1E10E52C2B83BC6D9E5BA83A4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_C2C413F2EC3E858386BFC6D9E5BB06D6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_65FB5CE1E10E52C2B83BC6D9E5BA83A4" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_C2C413F2EC3E858386BFC6D9E5BB06D6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_A2A63600E2A9684C1D10C6D9E5BB642D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E1AC7153C6A6743B03C5C6D9E5BB9422" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_A2A63600E2A9684C1D10C6D9E5BB642D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_013AFE325578CAA5ADF5C6FF9A1BD258" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E1AC7153C6A6743B03C5C6D9E5BB9422" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_013AFE325578CAA5ADF5C6FF9A1BD258" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_0447C09E5F0ED99A7701C6D9E5BB5722" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E1AC7153C6A6743B03C5C6D9E5BB9422" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_0447C09E5F0ED99A7701C6D9E5BB5722" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_85AA824A2859ADF659ABC6D9E5BB0CB6" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E1AC7153C6A6743B03C5C6D9E5BB9422" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_85AA824A2859ADF659ABC6D9E5BB0CB6" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationRestrictedStockUnitsNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B3C9298E3867CCBAC3CEA33E32FD25A2" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_DE26116257FC8E4FD212A33E32F26F86" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B3C9298E3867CCBAC3CEA33E32FD25A2" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_DE26116257FC8E4FD212A33E32F26F86" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_C2FCE71A7080F868076DA33E32F9A9A1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_DE26116257FC8E4FD212A33E32F26F86" xlink:to="loc_us-gaap_AwardTypeAxis_C2FCE71A7080F868076DA33E32F9A9A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9A22BE7A334D8A3ED20AA33E32F9B163_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_C2FCE71A7080F868076DA33E32F9A9A1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9A22BE7A334D8A3ED20AA33E32F9B163_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9A22BE7A334D8A3ED20AA33E32F9B163" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_C2FCE71A7080F868076DA33E32F9A9A1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9A22BE7A334D8A3ED20AA33E32F9B163" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_5A64C5EB089F42B770F8A33E337FA844" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9A22BE7A334D8A3ED20AA33E32F9B163" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_5A64C5EB089F42B770F8A33E337FA844" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_1BA2811856C08E49CFCEA33E32FA9844" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_DE26116257FC8E4FD212A33E32F26F86" xlink:to="loc_us-gaap_VestingAxis_1BA2811856C08E49CFCEA33E32FA9844" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_7C89AB782B8175524EF4A33E32FA7924_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_1BA2811856C08E49CFCEA33E32FA9844" xlink:to="loc_us-gaap_VestingDomain_7C89AB782B8175524EF4A33E32FA7924_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_7C89AB782B8175524EF4A33E32FA7924" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_1BA2811856C08E49CFCEA33E32FA9844" xlink:to="loc_us-gaap_VestingDomain_7C89AB782B8175524EF4A33E32FA7924" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_SharebasedCompensationAwardTrancheThreeMember" xlink:label="loc_rubi_SharebasedCompensationAwardTrancheThreeMember_DD4F6D7DD053F71B3DD7A33E33EE5FA2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_7C89AB782B8175524EF4A33E32FA7924" xlink:to="loc_rubi_SharebasedCompensationAwardTrancheThreeMember_DD4F6D7DD053F71B3DD7A33E33EE5FA2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_4E15A8D583EDA4704C5BA33E3312FDFF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B3C9298E3867CCBAC3CEA33E32FD25A2" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_4E15A8D583EDA4704C5BA33E3312FDFF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_826B2D3F83FCA14894D1A33E3321E338" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B3C9298E3867CCBAC3CEA33E32FD25A2" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_826B2D3F83FCA14894D1A33E3321E338" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_90C7F8BF43C4FBBD8A34A33E334B687F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_B3C9298E3867CCBAC3CEA33E32FD25A2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_90C7F8BF43C4FBBD8A34A33E334B687F" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationStockOptionsNarrativeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15D257282B9C64DD73A0C361C0986503" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15D257282B9C64DD73A0C361C0986503" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_C8449433EE6B224E6D35C361C0983447" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15D257282B9C64DD73A0C361C0986503" xlink:to="loc_us-gaap_AwardTypeAxis_C8449433EE6B224E6D35C361C0983447" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_85AC3F15B46B9FDAAE42C361C09822CB_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_C8449433EE6B224E6D35C361C0983447" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_85AC3F15B46B9FDAAE42C361C09822CB_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_85AC3F15B46B9FDAAE42C361C09822CB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_C8449433EE6B224E6D35C361C0983447" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_85AC3F15B46B9FDAAE42C361C09822CB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_5D1D7EB1BA1106F84271C361C0994140" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_85AC3F15B46B9FDAAE42C361C09822CB" xlink:to="loc_us-gaap_EmployeeStockOptionMember_5D1D7EB1BA1106F84271C361C0994140" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_01872F7449A42B8B2483C361C099B27F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15D257282B9C64DD73A0C361C0986503" xlink:to="loc_us-gaap_TitleOfIndividualAxis_01872F7449A42B8B2483C361C099B27F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_2C6C8C921287E33CBEFCC361C099BAD3_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_01872F7449A42B8B2483C361C099B27F" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_2C6C8C921287E33CBEFCC361C099BAD3_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_2C6C8C921287E33CBEFCC361C099BAD3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_01872F7449A42B8B2483C361C099B27F" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_2C6C8C921287E33CBEFCC361C099BAD3" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_NonEmployeeMember" xlink:label="loc_rubi_NonEmployeeMember_ECD8B75DE344108CB635C361C0999AA1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_2C6C8C921287E33CBEFCC361C099BAD3" xlink:to="loc_rubi_NonEmployeeMember_ECD8B75DE344108CB635C361C0999AA1" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_CertainEmployeesMember" xlink:label="loc_rubi_CertainEmployeesMember_4CA7EC89343C1EC7E92EC361C0998AD5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_2C6C8C921287E33CBEFCC361C099BAD3" xlink:to="loc_rubi_CertainEmployeesMember_4CA7EC89343C1EC7E92EC361C0998AD5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_8746A2123EC5E5C4862FC361C0994086" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_8746A2123EC5E5C4862FC361C0994086" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_41B6B9295AC0EED241BDC361C0997673" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_41B6B9295AC0EED241BDC361C0997673" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_A4281244D09A906219EBC361C0990B1A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_A4281244D09A906219EBC361C0990B1A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_6F0A303634602C96B7B9C361C09ACB53" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_6F0A303634602C96B7B9C361C09ACB53" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_8F07B2F51BA2FB39C4FEC361C09A0530" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_FEF932480EE90C4862DDC361C099C814" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_8F07B2F51BA2FB39C4FEC361C09A0530" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationStockOptionsOutstandingDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/StockBasedCompensationValuationAssumptionsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_20EECA186F88C131422C5729523D72E2" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FCEBB972457C02F5FDBC5729523CEBBE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_20EECA186F88C131422C5729523D72E2" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FCEBB972457C02F5FDBC5729523CEBBE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_5CB7DBDF985BCBF29EF45729523C108E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FCEBB972457C02F5FDBC5729523CEBBE" xlink:to="loc_us-gaap_AwardTypeAxis_5CB7DBDF985BCBF29EF45729523C108E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_05A4888EA77DC6C6E1535729523C1631_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_5CB7DBDF985BCBF29EF45729523C108E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_05A4888EA77DC6C6E1535729523C1631_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_05A4888EA77DC6C6E1535729523C1631" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_5CB7DBDF985BCBF29EF45729523C108E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_05A4888EA77DC6C6E1535729523C1631" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_703ADD86498725BB0A305729523CEE96" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_05A4888EA77DC6C6E1535729523C1631" xlink:to="loc_us-gaap_EmployeeStockOptionMember_703ADD86498725BB0A305729523CEE96" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_0784ECDA1BAE939827745729523CD1E6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_05A4888EA77DC6C6E1535729523C1631" xlink:to="loc_us-gaap_EmployeeStockMember_0784ECDA1BAE939827745729523CD1E6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_1A203857699FEA1B5C635729523D06FD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_20EECA186F88C131422C5729523D72E2" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_1A203857699FEA1B5C635729523D06FD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_F4C35F02AEB68B5800095729523DD10E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_20EECA186F88C131422C5729523D72E2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_F4C35F02AEB68B5800095729523DD10E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_427F3B1C1D869162515E5729523D8D11" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_20EECA186F88C131422C5729523D72E2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_427F3B1C1D869162515E5729523D8D11" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_DB466CA8836CECDD8FF65729523D198C" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_20EECA186F88C131422C5729523D72E2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_DB466CA8836CECDD8FF65729523D198C" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.rubiconproject.com/role/SubsequentEvents" xlink:type="extended" />
  <definitionLink xlink:role="http://www.rubiconproject.com/role/SubsequentEventsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:label="loc_us-gaap_SubsequentEventLineItems_2F5381B4A995FA232869C6D433365AC4" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SubsequentEventTable" xlink:label="loc_us-gaap_SubsequentEventTable_319EC1B33022C21DC473C6D433358C5B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_2F5381B4A995FA232869C6D433365AC4" xlink:to="loc_us-gaap_SubsequentEventTable_319EC1B33022C21DC473C6D433358C5B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_6BAA30089A494700A2F3C6D43336C969" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_319EC1B33022C21DC473C6D433358C5B" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_6BAA30089A494700A2F3C6D43336C969" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_1A076E0322C176B7F608C6D43336549A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_6BAA30089A494700A2F3C6D43336C969" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_1A076E0322C176B7F608C6D43336549A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_1A076E0322C176B7F608C6D43336549A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_6BAA30089A494700A2F3C6D43336C969" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_1A076E0322C176B7F608C6D43336549A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_A0750228CE3305F83342C6D5C8797FA0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_1A076E0322C176B7F608C6D43336549A" xlink:to="loc_us-gaap_SubsequentEventMember_A0750228CE3305F83342C6D5C8797FA0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_F1F039216D70B7267705C6DBD2BEE3AB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_319EC1B33022C21DC473C6D433358C5B" xlink:to="loc_us-gaap_PlanNameAxis_F1F039216D70B7267705C6DBD2BEE3AB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_94BBBD0FE05715DE960FC6DBD2D2F761_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_F1F039216D70B7267705C6DBD2BEE3AB" xlink:to="loc_us-gaap_PlanNameDomain_94BBBD0FE05715DE960FC6DBD2D2F761_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_94BBBD0FE05715DE960FC6DBD2D2F761" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_F1F039216D70B7267705C6DBD2BEE3AB" xlink:to="loc_us-gaap_PlanNameDomain_94BBBD0FE05715DE960FC6DBD2D2F761" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_A2014EquityIncentivePlanMember" xlink:label="loc_rubi_A2014EquityIncentivePlanMember_86605918434C24EA51DDC6E5F29069D5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_94BBBD0FE05715DE960FC6DBD2D2F761" xlink:to="loc_rubi_A2014EquityIncentivePlanMember_86605918434C24EA51DDC6E5F29069D5" xlink:type="arc" />
    <loc xlink:href="rubi-20141231.xsd#rubi_A2014EmployeeStockPurchasePlanMember" xlink:label="loc_rubi_A2014EmployeeStockPurchasePlanMember_1ADDE121E373DF9F01A3C6E62CD4D059" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_94BBBD0FE05715DE960FC6DBD2D2F761" xlink:to="loc_rubi_A2014EmployeeStockPurchasePlanMember_1ADDE121E373DF9F01A3C6E62CD4D059" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_FA95FE4A5763A7244D97C6DBF8C92E69" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_319EC1B33022C21DC473C6D433358C5B" xlink:to="loc_us-gaap_AwardTypeAxis_FA95FE4A5763A7244D97C6DBF8C92E69" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_48FEE7B683290BF7928EC6DBF8D00327_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_FA95FE4A5763A7244D97C6DBF8C92E69" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_48FEE7B683290BF7928EC6DBF8D00327_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_48FEE7B683290BF7928EC6DBF8D00327" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_FA95FE4A5763A7244D97C6DBF8C92E69" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_48FEE7B683290BF7928EC6DBF8D00327" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_AB5E108AAA215227889AC6E68A61BECB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_48FEE7B683290BF7928EC6DBF8D00327" xlink:to="loc_us-gaap_EmployeeStockMember_AB5E108AAA215227889AC6E68A61BECB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_C140A4C97CF68F5A1D3CC6D46861C77A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_2F5381B4A995FA232869C6D433365AC4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_C140A4C97CF68F5A1D3CC6D46861C77A" xlink:type="arc" />
  </definitionLink>
</linkbase>





