Exhibit 5.1


                         [Letterhead of Ross & Hardies]

                                  June 18, 2002

SPSS Inc.
233 South Wacker Drive
Chicago, Illinois  60601

          Re: Registration Statement on Form S-8

Ladies and Gentlemen:

          You have requested our opinion with respect to the registration by
SPSS Inc. ("SPSS" or the "Company") pursuant to a Registration Statement on Form
S-8 (the "Registration Statement") under the Securities Act of 1933, as amended
(the "Act"), of an aggregate of 1,000,000 shares of the Company's Common Stock,
$0.01 par value per share (the "Common Stock") issuable upon the exercise of
options (the "Options") to purchase Common Stock as issued pursuant to the SPSS
Inc. 2002 Equity Incentive Plan (the "2002 Plan").

          In so acting, we have examined originals or copies, certified or
otherwise identified to our satisfaction, of such documents, corporate records,
certificates of public officials and other instruments and have conducted such
other investigations of fact and law as we have deemed relevant and necessary to
form a basis for the opinions hereinafter expressed. In conducting such
examination, we have assumed (i) that all signatures are genuine, (ii) that all
documents and instruments submitted to us as copies conform with the originals,
and (iii) the due execution and delivery of all documents where due execution
and delivery are a prerequisite to the effectiveness thereof. As to any facts
material to this opinion, we have relied upon statements and representations of
officers and other representatives of the Company and certificates of public
officials and have not independently verified such facts, but have no actual
knowledge of the inaccuracy or incompleteness of the same.

          Based upon the foregoing, it is our opinion that the Common Stock
issuable upon the proper exercise of Options granted pursuant to the 2002 Plan
will be validly issued, fully paid and non-assessable when issued in accordance
with the 2002 Plan.

          We express no opinion as to the laws of any jurisdiction other than
the State of Illinois, the United States of America, and, solely with respect to
matters of corporate organization and authority, the General Corporation Law of
the State of Delaware. We are not admitted to the practice of law in the State
of Delaware. Accordingly, any opinion herein as to the corporation laws of the
State of Delaware is based solely upon the last general available compilation of
the statutes of State Law of Delaware published by Prentice Hall Law & Business.
Insofar as the foregoing opinion relates to matters that would be controlled by
the substantive laws of any jurisdiction other than the United States of
America, the General Corporation Law of the State of Delaware, with respect to
matters of corporate organization and authority, or the State of Illinois, we
have assumed that the substantive laws of such jurisdiction conform in all
respects to the internal laws of the State of Illinois.

          We hereby consent to the reference to our firm in the Registration
Statement relating to the registration of the 1,000,000 shares of Common Stock
issuable upon exercise of the Options described above.

                                            Very truly yours,

                                            /s/ David S. Guin
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                                            ROSS & HARDIES