Exhibit 32.1

CERTIFICATION PURSUANT TO
18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     In connection with the Quarterly Report of DealerTrack Holdings, Inc. (the “Company”) on Form 10-Q for the quarterly period ended September 30, 2006, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), we, Mark F. O’Neil, Chief Executive Officer of the Company, and Robert J. Cox, Chief Financial Officer of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to our knowledge:

     (1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

     (2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Mark F. O’Neil

Name: Mark F. O’Neil

Title: Chairman, President and Chief Executive Officer

Date: November 13, 2006

/s/ Robert J. Cox III

Name: Robert J. Cox III

Title: Senior Vice President, Chief Financial Officer and

Treasurer

Date: November 13, 2006

     A signed original of this written statement required by Section 906 of the Sarbanes-Oxley Act of 2002 has been provided to the Company and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request.