POWER OF ATTORNEY


	 KNOW ALL BY THESE PRESENTS, the undersigned
hereby constitutes and appoints ANDREA M. FIKE, NANCY E. FRASER, and
CHARLES M. OSBORNE, the undersigned's true and lawful attorney-in-fact to:


1. execute for and on behalf of the undersigned, in the
undersigned's capacity as an officer and / or director of Fair Isaac
Corporation (the "Company"), Forms 3, 4 and 5, including Form ID
application and verification, in accordance with Section 16(a) of the
Securities Exchange Act of 1934, as amended, and the rules and regulations
thereunder;

2. do and perform any and all acts for and on behalf of
the undersigned which may be necessary or desirable to complete and execute
any such Form ID, Form 3, 4 or 5 and timely file such form with the United
States Securities and Exchange Commission and any stock exchange or similar
authority; and

3. take any other action of any type whatsoever in
connection with the foregoing which, in the opinion of such
attorney-in-fact, may be of benefit to, in the best interest of, or legally
required by, the undersigned, it being understood that the documents
executed by such attorney-in-fact on behalf of the undersigned pursuant to
this Power of Attorney shall be in such form and shall contain such terms
and conditions as such attorney-in-fact may approve in such
attorney-in-fact's discretion.

	 The undersigned hereby grants to such
attorney-in-fact full power and authority to do and perform any and every
act and thing whatsoever requisite, necessary, or proper to be done in the
exercise of any of the rights and powers herein granted, as fully to all
intents and purposes as the undersigned might or could do if personally
present, with full power of substitution or revocation, hereby ratifying
and confirming all that such attorney-in-fact or
attorney-in-fact's
substitute or substitutes, shall lawfully do or cause to be done by virtue
of this Power of Attorney and the rights and powers herein granted. The
undersigned acknowledges that the foregoing attorney-in-fact, in serving in
such capacity at the request of the undersigned, is not assuming, nor is
the Company assuming, any of the undersigned's responsibilities to comply
with Section 16 of the Securities Exchange Act of 1934.

	This Power of
Attorney shall remain in full force and effect until the undersigned is no
longer required to file Forms 3, 4 and 5 with respect to the undersigned's
holdings of and transactions in securities issued by the Company, unless
earlier revoked by the undersigned in a signed writing delivered to the
foregoing attorney-in-fact.

	IN WITNESS WHEREOF, the undersigned has
caused the Power of Attorney to be executed as of this 18th day of
November, 2005.




Gregory M. Weitz