Exhibit 5.1



                    [MAYER, BROWN, ROWE & MAW LLP LETTERHEAD]




June 15, 2007

SPSS Inc.
233 South Wacker Drive
Chicago, Illinois  60606





Ladies and Gentlemen:

         We have acted as your counsel in connection with the registration of
$150,000,000 aggregate principal amount of 2.50% Convertible Subordinated Notes
due 2012 (the "Notes") issued by SPSS Inc., a Delaware corporation (the
"Company"), and the shares of common stock, $0.01 par value per share, of the
Company into which the Notes may be converted (the "Shares"). The Notes were
issued pursuant to an indenture, dated as of March 19, 2007, between the
Company, as issuer, and LaSalle Bank National Association, as trustee (the
"Indenture"). The Notes and the Shares may be sold from time to time by the
holders thereof.

         In rendering the opinions expressed herein, we have examined and relied
upon such documents, corporate records, certificates of public officials and
certificates as to factual matters executed by officers of the Company as we
have deemed necessary or appropriate. We have assumed the authenticity, accuracy
and completeness of all documents, records, and certificates submitted to us as
originals, the conformity to the originals of all documents, records and
certificates submitted to us as copies and the authenticity, accuracy and
completeness of the originals of all documents, records and certificates
submitted to us as copies. We have also assumed the legal capacity and
genuineness of the signatures of persons signing all documents in connection
with which the opinions expressed herein are rendered.

         Based upon and subject to the foregoing and to the limitations set
forth herein, we are of the opinion that:

                  (i) The Notes constitute valid and binding obligations of the
         Company enforceable against the Company in accordance with their terms,
         except as such enforceability may be limited by bankruptcy, insolvency,
         fraudulent conveyance, reorganization or similar laws affecting
         creditors' rights generally and subject to general principles of
         equity.



SPSS Inc.
June 15, 2007
Page 2

                  (ii) The Shares, when issued upon conversion of the Notes in
         accordance with the terms of the Notes and the Indenture, will be
         validly issued, fully paid and non-assessable.

         We hereby consent to the filing of this opinion letter as an exhibit to
the registration statement covering resales of the Notes and the Shares and to
the reference to this firm under the caption "Legal Matters" contained therein.

                                             Very truly yours,


                                             /s/ MAYER, BROWN, ROWE & MAW LLP


                                             MAYER, BROWN, ROWE & MAW LLP