EXHIBIT 5.1

                   [Letterhead of Gibson, Dunn & Crutcher LLP]

                                November 13,1999

Cadence Design Systems, Inc.
2655 Seely Avenue, Building 5
San Jose, CA 95134

         Re:      Registration Statement on Form S-8
                  OF CADENCE DESIGN SYSTEMS, INC.
                  -------------------------------

Ladies and Gentlemen:

         We refer to the registration statement on Form S-8 ("Registration
Statement"), under the Securities Act of 1933, as amended (the "Securities
Act"), filed by Cadence Design Systems, Inc., a Delaware corporation (the
"Company"), with respect to the proposed offering by the Company of up to
20,000,000 shares (the "Shares") of the common stock of the Company, $0.01 par
value per share (the "Common Stock"), subject to issuance by the Company upon
exercise of options granted under the 2000 Amended and Restated NonStatutory
Equity Incentive Plan (the "Plan").

         We have examined the originals or certified copies of such corporate
records, certificates of officers of the Company and/or public officials and
such other documents and have made such other factual and legal investigations
as we have deemed relevant and necessary as the basis for the opinions set forth
below. In such examination, we have assumed the genuineness of all signatures,
the authenticity of all documents submitted to us as originals, the conformity
to original documents of all documents submitted to us as conformed or
photostatic copies and the authenticity of the originals of such copies.

         Based on our examination mentioned above, subject to the assumptions
stated above and relying on the statements of fact contained in the documents
that we have examined, we are of the opinion that (i) the issuance by the
Company of the Shares has been duly authorized and (ii) when issued in
accordance with the terms of the Plan, the Shares will be duly and validly
issued, fully paid and non-assessable shares of Common Stock (except as to
shares issued pursuant to certain deferred payment arrangements, which will be
fully paid and nonassessable when such deferred payments are made in full).

         We are admitted to practice in the State of California, and are not
admitted to practice in the State of Delaware. However, for the limited purposes
of our opinion set forth above, we are generally familiar with the General
Corporation Law of the State of Delaware (the "DGCL") as presently in effect and
have made such inquiries as we consider necessary to render this opinion with
respect to a Delaware corporation. This opinion letter is limited to the laws of
the State of California and, to the limited extent set forth above, the DGCL, as
such laws presently exist and to the facts as they presently exist. We express
no opinion with respect to the effect or applicability of the laws of any other
jurisdiction. We assume no obligation to revise or supplement this opinion
letter should the laws of such jurisdictions be changed after the date hereof by
legislative action, judicial decision or otherwise.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. In giving this consent, we do not admit that we are
within the category of persons whose consent is required under Section 7 of the
Securities Act or the General Rules and Regulations of the Securities and
Exchange Commission.

                                                  Very truly yours,

                                                  /s/GIBSON, DUNN & CRUTCHER LLP