SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* Mandal Sumant (Last) (First) (Middle) 725 ARIZONA AVENUE SUITE 304 (Street) SANTA MONICA CA 90401 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol RUBICON PROJECT, INC. [ RUBI ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X Director 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 05/27/2015
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) X Form filed by One Reporting Person Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	05/27/2015		J(1)		1,360	D	$17.27(2)	26,969(3)	D
Common Stock								5,669,981(4)	I	See Footnote (4)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. On May 27, 2015, the reporting person transferred a total of 1,360 shares of Common Stock of the Issuer (the "Shares") to certain lenders in connection with the repayment of outstanding loans.

2. Reflects the closing sale price of the Shares on May 27, 2015, as reported by the New York Stock Exchange.

3. Reflects (i) 2,160 Shares received by the reporting person on May 27, 2015 in connection with pro-rata distributions-in-kind of Shares for no consideration, and (ii) 26,169 Shares received by the reporting person in the form of restricted stock awards in connection with his service as a director of the Issuer. The aforementioned distributions were made in accordance with the exemptions afforded by Rule 16a-13 and Rule 16a-9 of the Securities Exchange Act of 1934, as amended.

4. Represents i) 5,570,406 Shares directly beneficially owned by Clearstone Venture Partners III-A, L.P., a Delaware limited partnership ("CVP III-A") and ii) 99,576 Shares directly beneficially owned by Clearstone Venture Partners III-B, a Delaware Multi-Series LLC ("CVP III-B" and, together with CVP III-A, the "Funds"). Clearstone Venture Management III, LLC, a Delaware limited liability company ("CVM III") is the general partner and managing member of CVP III-A and CVP III-B, respectively. The reporting person is a managing member of CVM III and a member of CVP III-B. The reporting person disclaims beneficial ownership of the Shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and the inclusion of these Shares in this report shall not be deemed an admission of beneficial ownership of the reported shares for purposes of Section 16 or for any other purpose.

	Sumant Mandal	05/29/2015
	** Signature of Reporting Person	Date
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* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
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