Filed by Art Technology Group, Inc. pursuant to Rule 425 under the Securities
      Act of 1933, as amended and deemed filed pursuant to Rule 14a-12 under the
                                     Securities Exchange Act of 1934, as amended



                             Subject Company: Primus Knowledge Solutions, Inc.
                                                 Commission File No. 000-26273



Art Technology Group, Inc. has posted on its website a letter from its president
and chief executive officer that includes information about its proposed
acquisition of Primus Knowledge Solutions, Inc. The letter is attached as
Exhibit 99.1 and incorporated herein by reference.

ATG has filed a registration statement on Form S-4 in connection with the
transaction, and ATG and Primus intend to mail a joint proxy
statement/prospectus to their respective stockholders in connection with the
transaction. Investors and security holders of ATG and Primus are urged to read
the joint proxy statement/prospectus when it becomes available because it will
contain important information about ATG, Primus and the transaction. Investors
and security holders may obtain a free copy of the joint proxy
statement/prospectus (when it is available) at the SEC's web site at
www.sec.gov. A free copy of the joint proxy statement/prospectus may also be
obtained (when it is available) from ATG or Primus. Each of ATG and Primus also
files annual, quarterly and special reports, proxy and information statements,
and other information with the SEC. Investors may read and copy any of these
reports, statements and other information at the SEC's public reference rooms
located at 450 5th Street, N.W., Washington, D.C., 20549, or any of the SEC's
other public reference rooms. Investors should call the SEC at 1-800-SEC-0330
for further information on these public reference rooms. The reports, statements
and other information filed by ATG and Primus with the SEC are also available
for free at the SEC's web site at www.sec.gov. A free copy of these reports,
statements and other information may also be obtained from ATG or Primus.
The executive officers and directors of each of ATG and Primus may be deemed to
be participants in the solicitation of proxies from the stockholders of Primus
and ATG in favor of the Merger. A description of the interests of ATG's
executive officers and directors in ATG is set forth in the proxy statement for
ATG's 2004 Annual Meeting of Stockholders, which was filed with the SEC. A
description of the interests of Primus's executive officers and directors in
Primus is set forth in the proxy statement for Primus's 2004 Annual Meeting of
Stockholders, which was filed with the SEC. Investors and security holders may
obtain more detailed information regarding the direct and indirect interests of
ATG's and Primus' executive officers and directors in the Merger by reading the
preliminary joint proxy statement/prospectus filed with the SEC when it becomes
available.