<SEC-DOCUMENT>0001595974-16-000052.txt : 20161103
<SEC-HEADER>0001595974-16-000052.hdr.sgml : 20161103
<ACCEPTANCE-DATETIME>20161103174552
ACCESSION NUMBER:		0001595974-16-000052
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20161020
FILED AS OF DATE:		20161103
DATE AS OF CHANGE:		20161103

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			RUBICON PROJECT, INC.
		CENTRAL INDEX KEY:			0001595974
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMPUTER PROGRAMMING, DATA PROCESSING, ETC. [7370]
		IRS NUMBER:				208881738
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		12181 BLUFF CREEK DRIVE, 4TH FLOOR
		CITY:			LOS ANGELES
		STATE:			CA
		ZIP:			90094
		BUSINESS PHONE:		310-207-0272

	MAIL ADDRESS:	
		STREET 1:		12181 BLUFF CREEK DRIVE, 4TH FLOOR
		CITY:			LOS ANGELES
		STATE:			CA
		ZIP:			90094

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Richter James Neal
		CENTRAL INDEX KEY:			0001680756

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-36384
		FILM NUMBER:		161973017

	MAIL ADDRESS:	
		STREET 1:		C/O THE RUBICON PROJECT, INC.
		STREET 2:		12181 BLUFF CREEK DRIVE, 4TH FL
		CITY:			LOS ANGELES
		STATE:			CA
		ZIP:			90094
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_147820953963294.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-10-20</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001595974</issuerCik>
        <issuerName>RUBICON PROJECT, INC.</issuerName>
        <issuerTradingSymbol>RUBI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001680756</rptOwnerCik>
            <rptOwnerName>Richter James Neal</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O THE RUBICON PROJECT, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>12181 BLUFF CREEK DRIVE, 4TH FL</rptOwnerStreet2>
            <rptOwnerCity>LOS ANGELES</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>90094</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Technology Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>117316</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>4.7</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-12-07</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>14500.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>4.7</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-05-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>35499.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35499</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>16.75</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2025-05-19</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15800.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15800</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents: (i) 29,948 shares of restricted stock that vest as follows: 7,812 on November 15, 2016, 7,813 on May 15, 2017, 7,812 on November 15, 2017, and 6,511 on May 15, 2018; (ii) 29,357 restricted stock units that vest as follows: 5,338 on November 15, 2017, 5,337 on May 15, 2017, 5,338 on November 15, 2017, 5,337 on May 15, 2018, 5,338 on November 15, 2018, and 2,669 on May 15, 2019; (iii) 50,000 RSUs that vest as follows: 15,625 on May 15, 2017, 6,250 on each November 15 and May 15 thereafter until November 15, 2019, and 3,125 on May 15, 2020; and (iv) 8,011 shares of common stock.</footnote>
        <footnote id="F2">The option, originally representing a right to purchase a total of 20,000 shares, became exercisable with respect to 25% of the grant on October 27, 2012 and became exercisable with respect to the remainder in 36 equal installments each calendar month thereafter and is now fully vested.</footnote>
        <footnote id="F3">The option, originally representing a right to purchase a total of 79,999 shares, became exercisable with respect to 25% of the grant on April 1, 2013 and became exercisable with respect to the remainder in 36 equal installments each calendar month thereafter and is now fully vested.</footnote>
        <footnote id="F4">The option, representing a right to purchase a total of 15,800 shares, became exercisable with respect to 25% of the grant on February 1, 2016 and becomes exercisable with respect to the remainder in 36 equal installments each calendar month thereafter.</footnote>
    </footnotes>

    <remarks>Due to organizational changes, as of October 20, 2016, the reporting person is no longer an officer for purposes of Section 16 and therefore the reporting person will no longer report any transactions in the equity securities of the Issuer on Form 4 or Form 5.</remarks>

    <ownerSignature>
        <signatureName>Jonathan Feldman, attorney-in-fact</signatureName>
        <signatureDate>2016-11-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
