Exhibit 5.1


                           Simpson Thacher & Bartlett
                              425 Lexington Avenue
                            New York, New York 10017






                                                      January 9, 2003



Cognizant Technology Solutions Corporation
500 Glenpointe Centre West
Teaneck, New Jersey  07666

Ladies and Gentlemen:

      We have acted as counsel to Cognizant Technology Solutions Corporation, a
Delaware corporation (the "Company"), in connection with the Registration
Statement on Form S-4 (the "Registration Statement") filed by the Company with
the Securities and Exchange Commission (the "Commission") under the Securities
Act of 1933, as amended (the "Act"), relating to the offer by IMS Health
Incorporated ("IMS Health") to exchange up to 11,290,900 shares (the "Shares")
of the Company's Class B Common Stock, $.01 par value per share, that IMS
currently owns for a number of shares of outstanding common stock of IMS Health
to be specified (such offer, as it may be amended and supplemented from time to
time, the "Exchange Offer").

      We have examined the Registration Statement and a form of the share
certificate, which has been filed with the Commission as an exhibit to the
Registration Statement. We also have examined the originals, or duplicates or
certified or conformed copies, of such records, agreements, instruments and
other documents and have made such other and further investigations as we have
deemed relevant and necessary in connection with the opinions expressed herein.
As to questions of fact material to this opinion, we have relied upon
certificates of public officials and of officers and representatives of the
Company.

      In such examination, we have assumed the genuineness of all signatures,
the legal capacity of natural persons, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as duplicates or certified or conformed copies, and
the authenticity of the originals of such latter documents.

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      Based upon the foregoing, and subject to the qualifications and
limitations stated herein, we are of the opinion that Shares have been validly
issued and fully paid and are nonassessable.


      We are members of the Bar of the State of New York and we do not express
any opinion herein concerning any law other than the Delaware General
Corporation Law (including the statutory provisions, all applicable provisions
of the Delaware Constitution and reported judicial decisions interpreting the
foregoing).


      We hereby consent to the filing of this opinion letter as Exhibit 5.1 to
the Registration Statement and to the use of our name under the caption "Legal
Matters" in the Prospectus included in the Registration Statement.


                                          Very truly yours,

                                          /s/ Simpson Thacher & Bartlett

                                          SIMPSON THACHER & BARTLETT