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                                                                   EXHIBIT 10.29

                       SEVENTH LOAN MODIFICATION AGREEMENT

      This Seventh Loan Modification Agreement (this "Loan Modification
Agreement") is entered into as of December 21, 2004, by and between SILICON
VALLEY BANK, a California-chartered bank, with its principal place of business
at 3003 Tasman Drive, Santa Clara, California 95054 and with a loan production
office located at One Newton Executive Park, Suite 200, 2221 Washington Street,
Newton, Massachusetts 02462, doing business under the name "Silicon Valley East"
("Bank") and ART TECHNOLOGY GROUP, INC., a Delaware corporation with its
principal place of business at 25 First Street, Cambridge, Massachusetts 02141
("Borrower").

1.    DESCRIPTION OF EXISTING INDEBTEDNESS AND OBLIGATIONS. Among other
      indebtedness and obligations which may be owing by Borrower to Bank,
      Borrower is indebted to Bank pursuant to a loan arrangement dated as of
      June 13, 2002, evidenced by, among other documents, a certain Amended and
      Restated Loan and Security Agreement dated as of June 13, 2002, between
      Borrower and Bank, as amended by a certain First Loan Modification
      Agreement dated as of September 27, 2002, as further amended by a certain
      Amendment dated as of October __, 2002, as further amended by a certain
      Second Loan Modification Agreement dated as of December 24, 2002, as
      further amended by a certain Third Loan Modification Agreement dated as of
      October 20, 2003, as further amended by a certain Fourth Loan Modification
      Agreement dated November 26, 2003, as further amended by a certain Letter
      Agreement dated June 16, 2004, as further amended by a certain Fifth Loan
      Modification Agreement dated June 30, 2004, and as further amended by a
      certain Sixth Loan Modification Agreement dated November 24, 2004 (as
      amended, the "Loan Agreement"). Capitalized terms used but not otherwise
      defined herein shall have the same meaning as in the Loan Agreement.

2.    DESCRIPTION OF COLLATERAL. Repayment of the Obligations is secured by the
      Collateral as described in the Loan Agreement (together with any other
      collateral security granted to Bank, the "Security Documents").

Hereinafter, the Security Documents, together with all other documents
evidencing or securing the Obligations shall be referred to as the "Existing
Loan Documents".

3.    DESCRIPTION OF CHANGE IN TERMS.

      Modifications to Loan Agreement.

            1.    The Loan Agreement shall be amended by deleting the following
                  text appearing in Section 2.4(e) thereof:

                        "(e) Compensating Balance/Compensating Balances Fees. In
                        the event, at any time, Borrower maintains less than
                        $25,000,000 in unrestricted cash (including, without
                        limitation, cash, cash equivalents and marketable
                        securities) with Bank, Borrower shall pay such fees and
                        expenses as Bank shall determine, in its sole and
                        exclusive discretion, to compensate Bank for its loss on
                        income on such deposit balance (the "Additional Fees")."

                  and inserting in lieu thereof the following:

                        "(e) Compensating Balance/Compensating Balances Fees. In
                        the event, at any time, Borrower maintains, at any time,
                        an amount less than two (2) times the

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                        amount of the outstanding Obligations, at any time, in
                        unrestricted cash (including, without limitation, cash,
                        cash equivalents and marketable securities) with Bank,
                        Borrower shall pay such fees and expenses as Bank shall
                        determine, in its sole and exclusive discretion, to
                        compensate Bank for its loss on income on such deposit
                        balance (the "Additional Fees")."

            2.    The Loan Agreement shall be amended by deleting the following
                  text, appearing in Section 6.7 thereof:

                        "(a) LIQUIDITY. Borrower shall have at all times, to be
                        tested as of the last day of each month, unrestricted
                        and unencumbered cash (including, without limitation,
                        cash, cash equivalents and marketable securities) equal
                        to or greater than $25,000,000.00.

                        (b) PROFITABILITY. Borrower shall have quarterly net
                        losses of not more than (i) $3,500,000.00 for the
                        quarter ending December 31, 2003; (ii) $3,000,000.00 for
                        the quarter ending March 31, 2004; (iii) $5,000,000.00
                        for the quarter ending June 30, 2004; (iv) $2,000,000.00
                        for the quarter ending September 30, 2004; (v)
                        $1,000,000.00 for each quarter thereafter"

                  an inserting in lieu thereof the following:

                        "(a) LIQUIDITY. Borrower shall have at all times, to be
                        tested as of the last day of each month, minimum
                        unrestricted and unencumbered cash (including, without
                        limitation, cash, cash equivalents and marketable
                        securities) in an amount equal to: (i) for the months
                        ending January 31, 2005, February 28, 2005, April 30,
                        2005 and May 31, 2005, the greater of (A) Fifteen
                        Million Dollars ($15,000,000.00) and (B) two (2) times
                        the amount of the Obligations, and (ii) ) for months
                        ending March 31, 2005 and June 30, 2005, and as of the
                        last day of each month thereafter Twenty Million Dollars
                        ($20,000,000.00).

                        (b) PROFITABILITY. Borrower shall have quarterly: (i)
                        net losses of not more than (A) $4,500,000.00 for the
                        quarter ending December 31, 2004; (B) $2,000,000.00 for
                        the quarter ending March 31, 2005; (C) $500,000.00 for
                        the quarter ending June 30, 2005; (D) $1,500,000.00 for
                        the quarter ending September 30, 2005; and (ii) net
                        profit of at least One Dollar ($1.00) for the quarter
                        ending December 31, 2005, and as of the last day of each
                        quarter thereafter."

            3.    The Loan Agreement shall be amended by deleting the following
                  definitions appearing in Section 13 thereof, in their
                  entirety:

                        ""GUARANTOR" is any present or future guarantor of the
                        Obligations, including Art Technology Group (Europe)
                        Limited.

                        ""OBLIGATIONS" are debts, principal, interest, Bank
                        Expenses and other amounts Borrower owes Bank now or
                        later, including letters of credit, cash management
                        services, and foreign exchange contracts, if any, and
                        including interest accruing after Insolvency Proceedings
                        begin and debts, liabilities, or obligations of Borrower
                        assigned to Bank."

                        "REVOLVING MATURITY DATE" is December 25, 2004."

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                  and inserting in lieu thereof the following:

                        ""GUARANTOR" is any present or future guarantor of the
                        Obligations, including but not limited to Primus
                        Knowledge Solutions, Inc."

                        ""OBLIGATIONS" are debts, principal, interest, Bank
                        Expenses and other amounts Borrower owes Bank now or
                        later, including letters of credit (including the
                        aggregate amount of undrawn letters of credit), cash
                        management services, and foreign exchange contracts, if
                        any, and including interest accruing after Insolvency
                        Proceedings begin and debts, liabilities, or obligations
                        of Borrower assigned to Bank."

                        "REVOLVING MATURITY DATE" is December 24, 2005."

4.    FEES. Borrower shall pay to Bank a modification fee equal to Seventy-Five
      Thousand Dollars and 00/100 ($75,000.00), which fee shall be due on the
      date hereof and shall be deemed fully earned as of the date hereof. The
      Borrower shall also reimburse Bank for all reasonable legal fees and
      expenses incurred in connection with this amendment to the Existing Loan
      Documents.

5.    RATIFICATION OF INTELLECTUAL PROPERTY SECURITY AGREEMENT. Borrower hereby
      ratifies, confirms and reaffirms, all and singular, the terms and
      conditions of a certain Intellectual Property Security Agreement dated as
      of June 13, 2002 between Borrower and Bank, and acknowledges, confirms and
      agrees that said Intellectual Property Security Agreement contains an
      accurate and complete listing of all Intellectual Property Collateral as
      defined in said Intellectual Property Security Agreement (with the
      exception of the Intellectual Property Collateral set forth on Schedule 5
      attached hereto) as of June 13, 2002 or any subsequent amendment thereto
      and shall remain in full force and effect.

6.    RATIFICATION OF PERFECTION CERTIFICATE. Borrower hereby ratifies, confirms
      and reaffirms, all and singular, the terms and disclosures contained in a
      certain Perfection Certificate dated as of June 13, 2002 between Borrower
      and Bank, and acknowledges, confirms and agrees the disclosures and
      information Borrower provided to Bank in said Perfection Certificate has
      not changed, as of the date hereof.

7.    CONSISTENT CHANGES. The Existing Loan Documents are hereby amended
      wherever necessary to reflect the changes described above.

8.    RATIFICATION OF LOAN DOCUMENTS. Borrower hereby ratifies, confirms, and
      reaffirms all terms and conditions of all security or other collateral
      granted to the Bank, and confirms that the indebtedness secured thereby
      includes, without limitation, the Obligations.

9.    NO DEFENSES OF BORROWER. Borrower agrees that, as of this date, it has no
      defenses against the obligations to pay any amounts under the Obligations.

10.   CONTINUING VALIDITY. Borrower understands and agrees that in modifying the
      existing Obligations, Bank is relying upon Borrower's representations,
      warranties, and agreements, as set forth in the Existing Loan Documents.
      Except as expressly modified pursuant to this Loan Modification Agreement,
      the terms of the Existing Loan Documents remain unchanged and in full
      force and effect. Bank's agreement to modifications to the existing
      Obligations pursuant to this Loan Modification Agreement in no way shall

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      obligate Bank to make any future modifications to the Obligations. Nothing
      in this Loan Modification Agreement shall constitute a satisfaction of the
      Obligations. It is the intention of Bank and Borrower to retain as liable
      parties all makers of Existing Loan Documents, unless the party is
      expressly released by Bank in writing. No maker will be released by virtue
      of this Loan Modification Agreement.

11.   COUNTERSIGNATURE. This Loan Modification Agreement shall become effective
      only when it shall have been executed by Borrower and Bank (provided,
      however, in no event shall this Loan Modification Agreement become
      effective until signed by an officer of Bank in California).

                  [Remainder of page intentionally left blank]

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      This Loan Modification Agreement is executed as a sealed instrument under
the laws of the Commonwealth of Massachusetts as of the date first written
above.

BORROWER:                        BANK:

ART TECHNOLOGY GROUP, INC.       SILICON VALLEY BANK, doing business as
                                 SILICON VALLEY EAST

By: /s/ Edward Terino            By: /s/ Michael D. Sinclair
    -------------------------        --------------------------------

Name: Edward Terino              Name: Michael D. Sinclair

Title: CFO                       Title: Vice President
          12/21/04

                                 SILICON VALLEY BANK

                                 By: /s/ Jacquelyne Le
                                     -------------------------------

                                 Name: Jacquelyne Le

                                 Title: Operations Supervisor
                                  (signed in Santa Clara County, California)