Exhibit 5.1

[LETTERHEAD OF SKADDEN, ARPS, SLATE, MEAGHER & FLOM LLP]

March 18, 2014

Ladies and Gentlemen:

We have acted as special counsel to BlackRock, Inc., a Delaware corporation (the “Company”), in connection with the public offering of $1,000,000,000 aggregate principal amount of the Company’s 3.500% Notes Due 2024 (collectively, the “Securities”), issuable under the Indenture, dated as of September 17, 2007 (the “Indenture”), between the Company and The Bank of New York Mellon (formerly known as The Bank of New York), as trustee (the “Trustee”). On March 13, 2014, the Company entered into an Underwriting Agreement (the “Underwriting Agreement”), with Deutsche Bank Securities Inc., HSBC Securities (USA) Inc., Merrill Lynch, Pierce, Fenner & Smith Incorporated and Morgan Stanley & Co. LLC, as representatives of the several underwriters named therein (the “Underwriters”), relating to the sale by the Company to the Underwriters of the Securities.

This opinion is being delivered in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act of 1933, as amended (the “Securities Act”).

In rendering the opinion set forth herein, we have examined and relied upon the following:

(i) the registration statement on Form S-3 (File No. 333-191157) of the Company, relating to the Securities and other securities of the Company, filed

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on September 13, 2013 with the Securities and Exchange Commission (the “Commission”) under the Securities Act, allowing for delayed offerings pursuant to Rule 415 of the General Rules and Regulations under the Securities Act (the “Rules and Regulations”), including information deemed to be a part of the registration statement pursuant to Rule 430B of the Rules and Regulations (such registration statement, which became effective upon filing pursuant to Rule 462(e) of the Rules and Regulations, being hereinafter referred to as the “Registration Statement”)

(ii) the executed copies of the certificates evidencing the Securities (the “Note Certificates”) in the form delivered by the Company to the Trustee for authentication and delivery;

(iii) an executed copy of the Indenture;

(iv) an executed copy of the Officers’ Certificate establishing the form and terms of the Securities pursuant to Sections 102, 301 and 303 of the Indenture;

(v) a copy of the Company’s Amended and Restated Certificate of Incorporation, as amended and in effect as of the date hereof, certified by the Secretary of State of the State of Delaware as of March 13, 2014, certified pursuant to the Secretary’s Certificate;

(vi) the Amended and Restated By-Laws of the Company, as amended and in effect as of the date hereof, certified by the Assistant Secretary of the Company;

(vii) a copy of certain resolutions of the Board of Directors of the Company, adopted on July 27, 2007, January 16, 2013, July 24, 2013 and January 15, 2014, certified by the Assistant Secretary of the Company.

We have also examined originals or copies, certified or otherwise identified to our satisfaction, of such records of the Company and such agreements, certificates and receipts of public officials, certificates of officers or other representatives of the Company and others, and such other documents as we have deemed necessary or appropriate as a basis for the opinions stated below.

In our examination, we have assumed the genuineness of all signatures, including endorsements, the legal capacity and competency of all natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as facsimile, electronic, certified or photostatic copies, and the authenticity of the originals of such copies. As to any facts relevant to the opinions stated herein that we did not independently establish or verify, we have relied upon statements and representations of officers and other representatives of the Company and others and of public officials.

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We do not express any opinion with respect to the laws of any jurisdiction other than (i) the General Corporation Law of the State of Delaware and (ii) those laws, rules and regulations of the State of New York that, in our experience, are normally applicable to transactions of the type contemplated by the Transaction Agreements, and, to the extent that judicial or regulatory orders or decrees or consents, approvals, licenses, authorizations, validations, filings, recordings or registrations with governmental authorities are relevant, to those required under such laws (all of the foregoing being referred to as “Opined on Law”). We do not express any opinion as to the effect of any non-Opined on Law on the opinions stated herein. Insofar as the opinion expressed herein relates to matters governed by laws other than those set forth in the preceding sentence, we have assumed, without having made any independent investigation, that such laws do not affect the opinion set forth herein. The opinion expressed herein is based on laws in effect on the date hereof, which laws are subject to change with possible retroactive effect.

Based upon the foregoing and subject to the limitations, qualifications, exceptions and assumptions set forth herein, we are of the opinion that the Securities have been duly authorized and executed by the Company, will constitute valid and binding obligations of the Company entitled to the benefits of the Indenture and enforceable against the Company in accordance with their terms.

The opinions stated herein are subject to the following qualifications:

(a) the validity or enforcement of any agreements or instruments may be limited by applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent transfer, preference and other similar laws affecting creditors’ rights generally and by general principles of equity (regardless of whether enforcement is sought in equity or at law);

(b) except to the extent expressly stated in the opinion contained herein with respect to the Company and the Securities, we do not express any opinion with respect to the effect on the opinion stated herein of (i) the compliance or non-compliance of any party to the Indenture with any laws, rules or regulations applicable to such party or (ii) the legal status or legal capacity of any such party to the Indenture;

(c) except to the extent expressly stated in the opinions contained herein with respect to the Company and the Securities, we do not express any opinion with respect to any law, rule or regulation that is applicable to any party to the Indenture or the transactions contemplated thereby solely because such law, rule

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or regulation is part of a regulatory regime applicable to any such party or any of its affiliates as a result of the specific assets or business operations of such party or such affiliates;

(d) to the extent that any opinion relates to the enforceability of the choice of New York law and choice of New York forum provisions contained in the Underwriting Agreement, the Indenture or the Note Certificates, the opinions stated herein are subject to the qualification that such enforceability may be subject to, in each case, (i) the exceptions and limitations in New York General Obligations Law sections 5-1401 and 5-1402 and (ii) principles of comity or constitutionality;

(e) neither the execution and delivery by the Company of the Indenture and the Securities, as applicable, nor the consummation by the Company of its obligations thereunder: (i) constitutes or will constitute a violation of, or a default under, any lease, indenture, instrument or other agreement to which the Company or its property is subject, (ii) contravenes or will contravene any order or decree of any governmental authority to which the Company or any of its property is subject, or (iii) violates or will violate any law, rule or regulation to which the Company or any of its property is subject; and

(f) neither the execution and delivery by the Company of the Indenture and the Securities, as applicable, nor the consummation by the Company of its obligations thereunder, requires or will require the consent, approval, licensing or authorization of, or any filing, recording or registration with, any governmental authority under any law, rule or regulation of any jurisdiction.

We hereby consent to the filing of this opinion with the Commission as an exhibit to the Company’s Current Report on Form 8-K being filed on the date hereof, and incorporated by reference into the Registration Statement. We also hereby consent to the reference to our firm under the caption “Legal Matters” in the prospectus supplement, dated March 13, 2014, and filed with the Commission. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the Rules and Regulations. This opinion is expressed as of the date hereof unless otherwise expressly stated, and we disclaim any undertaking to advise you of any subsequent changes in the facts stated or assumed herein or of any subsequent changes in applicable law.