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* MAYFIELD XII A DELAWARE L P (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (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) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 02/26/2015
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X 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	02/26/2015		S		144,833	D	$19.1593(1)	3,844,539	D(3)(4)(5)
Common Stock	02/26/2015		S		2,240	D	$19.1593(1)	59,451	I(3)(4)(5)	By Mayfield Associates Fund XII
Common Stock	02/26/2015		S		2,240	D	$19.1593(1)	59,451	I(3)(4)(5)	By Mayfield Principals Fund XII
Common Stock	02/27/2015		S		89,640	D	$18.9346(2)	3,754,899	D(3)(4)(5)
Common Stock	02/27/2015		S		1,386	D	$18.9346(2)	58,065	I(3)(4)(5)	By Mayfield Associates Fund XII
Common Stock	02/27/2015		S		1,386	D	$18.9346(2)	58,065	I(3)(4)(5)	By Mayfield Principals Fund XII

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

1. Name and Address of Reporting Person* MAYFIELD XII A DELAWARE L P (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

1. Name and Address of Reporting Person* Mayfield XII Management, L.L.C. (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

1. Name and Address of Reporting Person* MAYFIELD ASSOCIATES FUND XII (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

1. Name and Address of Reporting Person* Mayfield Principals Fund XII (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

1. Name and Address of Reporting Person* Beck James T (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

1. Name and Address of Reporting Person* Chaddha Navin (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

1. Name and Address of Reporting Person* VASAN ROBERT T (Last) (First) (Middle) 2484 SAND HILL ROAD (Street) MENLO PARK CA 94025 (City) (State) (Zip)

Explanation of Responses:

1. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $19.00 to $19.96, inclusive. The Reporting Persons undertake to provide to The Rubicon Project, Inc., any security holder of The Rubicon Project, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (1) to this Form 4.

2. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $18.85 to $19.37, inclusive. The Reporting Persons undertake to provide to The Rubicon Project, Inc., any security holder of The Rubicon Project, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (2) to this Form 4.

3. Mayfield XII Management, L.L.C. ("MF XII Management") is the sole general partner of each of Mayfield XII, a Delaware Limited Partnership ("MF XII") and Mayfield Associates Fund XII, a Delaware Limited Partnership ("MF A XII"), and is the sole managing director of Mayfield Principals Fund XII, a Delaware Multiple Series LLC ("MF PF XII"), and in such capacity may be deemed to beneficially own the shares of common stock beneficially held by each of MF XII, MF A XII and MF PF XII. MF XII Management is managed by three managing directors, James T. Beck, Navin Chaddha and Robert T. Vasan, and all action by the managing directors relating to the voting or disposition of the shares of common stock beneficially held by each of MF XII, MF A XII and MF PF XII requires approval of a majority of the managing directors.

4. Each of James T. Beck, Navin Chaddha, and Robert T. Vasan, as the managing directors of MF XII Management, may be deemed to share beneficial ownership of the shares that are beneficially owned by MF XII Management, but each disclaims such beneficial ownership, except to the extent of his pecuniary interest therein.

5. The filing of this statement shall not be deemed an admission that, for the purposes of Section 16 of the Securities Act of 1934 or otherwise, the Reporting Persons are the beneficial owners of equity securities covered by this statement.

Remarks:

	James T. Beck, Authorized Signatory for Mayfield XII Management, L.L.C., the sole General Partner of Mayfield XII, a Delaware Limited Partnership	03/02/2015
	James T. Beck, Authorized Signatory for Mayfield XII Management, L.L.C.	03/02/2015
	James T. Beck, Authorized Signatory for Mayfield XII Management, L.L.C., the sole General Partner of Mayfield Associates Fund XII, a Delaware Limited Partnership	03/02/2015
	James T. Beck, Authorized Signatory for Mayfield XII Management, L.L.C., the Managing Director of Mayfield Principals Fund XII, a Delaware Multiple Series LLC	03/02/2015
	James T. Beck	03/02/2015
	James T. Beck, Attorney-In-Fact for Navin Chaddha	03/02/2015
	James T. Beck, Attorney-In-Fact for Robert T. Vasan	03/02/2015
	** Signature of Reporting Person	Date
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