<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2013-06-11</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001484504</issuerCik>
        <issuerName>Gigamon Inc.</issuerName>
        <issuerTradingSymbol>GIMO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001554026</rptOwnerCik>
            <rptOwnerName>Highland Management Partners VII, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HIGHLAND CAPITAL PARTNERS,</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BROADWAY, 16TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02142</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001343244</rptOwnerCik>
            <rptOwnerName>HIGHLAND CAPITAL PARTNERS VII-B L P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HIGHLAND CAPITAL PARTNERS,</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BROADWAY, 16TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02142</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001343673</rptOwnerCik>
            <rptOwnerName>Highland Capital Partners VII-C LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HIGHLAND CAPITAL PARTNERS,</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BROADWAY, 16TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02142</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001357840</rptOwnerCik>
            <rptOwnerName>Highland Entrepreneurs Fund VII Limited Partnership</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HIGHLAND CAPITAL PARTNERS,</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BROADWAY, 16TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02142</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001554027</rptOwnerCik>
            <rptOwnerName>Highland Management Partners VII Limited Partnership</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HIGHLAND CAPITAL PARTNERS,</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BROADWAY, 16TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02142</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001343678</rptOwnerCik>
            <rptOwnerName>Highland Capital Partners VII LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HIGHLAND CAPITAL PARTNERS,</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BROADWAY, 16TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02142</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Series A Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F5"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4985927</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Series A Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F5"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1208187</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Series A Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F5"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1759502</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Series A Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F5"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>156231</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The securities are held by Highland Capital Partners VII Limited Partnership (&quot;HCP VII&quot;).  Highland Management Partners VII, LLC (&quot;HMP VII LLC&quot;) is the general partner of Highland Management Partnership VII Limited Partnership (&quot;HMP VII LP&quot;), which is the general partner of HCP VII.  Each of HMP VII LP and HMP VII LLC disclaims beneficial ownership of all shares held by HCP VII except to the extent, if any, of such entity's pecuniary interest therein.</footnote>
        <footnote id="F2">The securities are held by Highland Capital Partners VII-B Limited Partnership (&quot;HCP VII-B&quot;).  HMP VII LP is the general partner of HCP VII-B.  Each of HMP VII LP and HMP VII LLC disclaims beneficial ownership of all shares held by HCP VII-B except to the extent, if any, of such entity's pecuniary interest therein.</footnote>
        <footnote id="F3">The securities are held by Highland Capital Partners VII-C Limited Partnership (&quot;HCP VII-C&quot;).  HMP VII LP is the general partner of HCP VII-C.  Each of HMP VII LP and HMP VII LLC disclaims beneficial ownership of all shares held by HCP VII-C except to the extent, if any, of such entity's pecuniary interest therein.</footnote>
        <footnote id="F4">The securities are held by Highland Entrepreneurs' Fund VII Limited Partnership (&quot;HEF VII&quot;).  HMP VII LP is the general partner of HEF VII.  Each of HMP VII LP and HMP VII LLC disclaims beneficial ownership of all shares held by HEF VII except to the extent, if any, of such entity's pecuniary interest therein.</footnote>
        <footnote id="F5">HCP VII is the holder of record of 4,985,927 shares of Series A preferred stock, which are convertible into 4,985,927 shares of common stock.  HCP VII-B is the holder of record of 1,208,187 shares of Series A preferred stock, which are convertible into 1,208,187 shares of common stock. HCP VII-C is the holder of record of 1,759,502 shares of Series A preferred stock, which are convertible into 1,759,502 shares of common stock.  HEF VII is the holder of record of 156,231 shares of Series A preferred stock, which are convertible into 156,231 shares of common stock.  The Series A preferred stock will convert into common stock immediately prior to the closing of the Issuer's initial public offering on a one-for-one basis, and has no expiration date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Corey Mulloy, Authorized Manager of Highland Management Partners VII, LLC</signatureName>
        <signatureDate>2013-06-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Corey Mulloy, Authorized Manager of Highland Management Partners VII, LLC, the general partner of Highland Management Partners VII Limited Partnership</signatureName>
        <signatureDate>2013-06-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Corey Mulloy, Authorized Manager of Highland Management Partners VII, LLC, the general partner of Highland Management Partners VII Limited Partnership, the general partner of Highland Capital Partners VII Limited Partnership</signatureName>
        <signatureDate>2013-06-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Corey Mulloy, Authorized Manager of Highland Management Partners VII, LLC, the general partner of Highland Management Partners VII Limited Partnership, the general partner of Highland Capital Partners VII-B Limited Partnership</signatureName>
        <signatureDate>2013-06-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Corey Mulloy, Authorized Manager of Highland Management Partners VII, LLC, the general partner of Highland Management Partners VII Limited Partnership, the general partner of Highland Capital Partners VII-C Limited Partnership</signatureName>
        <signatureDate>2013-06-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Corey Mulloy, Authorized Manager of Highland Management Partners VII, LLC, the general partner of Highland Management Partners VII Limited Partnership, the general partner of Highland Entrepreneurs' Fund VII Limited Partnership</signatureName>
        <signatureDate>2013-06-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
