Exhibit 5.1

[Letterhead of Wachtell, Lipton, Rosen & Katz]

April 2, 2018

salesforce.com, inc.

The Landmark @ One Market, Suite 300

San Francisco, California 94105

RE: Registration Statement on Form S-4 initially filed on April 2, 2018

Ladies and Gentlemen:

We have acted as special counsel to salesforce.com, inc., a Delaware corporation (the “Company”), in connection with the preparation and filing of the Registration Statement on Form S-4 of the Company (the “Registration Statement”, which term does not include any other document or agreement whether or not specifically referred to therein or attached as an exhibit or schedule thereto), relating to shares of common stock, par value $0.001 per share of the Company (the “Shares”), to be issued by the Company pursuant to the terms of the Agreement and Plan of Merger, dated as of March 20, 2018, by and among the Company, Malbec Acquisition Corp., a Delaware corporation and an indirect wholly owned subsidiary of the Company, and MuleSoft, Inc., a Delaware corporation (the “Merger Agreement”).

For the purposes of giving this opinion, we have examined the Registration Statement, the Merger Agreement and the amended and restated certificate of incorporation and amended and restated bylaws of the Company. We have also examined the originals, or duplicates or certified or conformed copies, of such corporate records, agreements, documents and other instruments and have made such other investigations as we have deemed relevant and necessary in connection with this opinion. As to questions of fact material to this opinion, we have relied, with your approval, upon oral and written representations of the Company and certificates or comparable documents of public officials and of officers and representatives of the Company.

In making such examination and rendering this opinion, we have assumed without verification the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the authenticity of the originals of such documents submitted to us as certified copies, the conformity to originals of all documents submitted to us as copies, the authenticity of the originals of such documents, that all documents submitted to us as certified copies are true and correct copies of such originals and the legal capacity of all individuals executing any of the foregoing documents.

Based upon and subject to the foregoing examination and in reliance thereon, and subject to the qualifications, assumptions and limitations stated herein and in reliance on statements of fact contained in the documents that we have examined or reviewed, we are of the opinion that the Shares to be issued by the Company pursuant to the terms of the Merger Agreement are or will be, upon issuance, duly authorized and, when the Registration Statement has been declared effective by order of the Securities and Exchange Commission and the Shares have been issued and paid for in the manner contemplated by and upon the terms and conditions set forth in the Registration Statement and the Merger Agreement, such Shares will be validly issued, fully paid and nonassessable.

This opinion is subject to the effects of (a) bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting the enforcement of creditors’ rights generally, (b) general equitable principles (whether considered in a proceeding in equity or at law) and (c) an implied covenant of good faith and fair dealing. We are members of the bar of the State of New York; the Company is a Delaware corporation, and we have not considered, and we express no opinion as to, 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 be named in the Registration Statement and in the related prospectus/offer to exchange contained therein as the attorneys who passed upon the legality of the Shares and to the filing of a copy of this opinion as Exhibit 5.1 to the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended, and the rules and regulations of the Securities and Exchange Commission promulgated thereunder. This opinion speaks as of its date, and we undertake no (and hereby disclaim any) obligation to update this opinion.

Very truly yours,

/s/ Wachtell, Lipton, Rosen & Katz