1875 K Street, N.W.

Washington, DC 20006

Tel: 202 303 1000

Fax: 202 303 2000

October 30, 2015

VIA EDGAR

Securities and Exchange Commission

100 F Street, NE

Washington, DC 20549

Re: iShares U.S. ETF Trust (the “Trust”)

(Securities Act File No. 333-179904

Investment Company Act File No. 811-22649)

Post-Effective Amendment No. 173

Ladies and Gentlemen:

On behalf of the Trust, we hereby transmit for filing under the Securities Act of 1933 (the “1933 Act”) and the Investment Company Act of 1940, Post-Effective Amendment No. 173 (the “Amendment”) to the Trust’s Registration Statement on Form N-1A. The Amendment relates to the following series of the Trust:

iShares iBonds Dec 2023 AMT-Free Muni Bond ETF (the “Fund”)

The Amendment is being filed pursuant to Rule 485(a)(2) under the 1933 Act for the sole purpose of adding a new series to the Trust, and it will become automatically effective 75 days after the filing.

The following information is provided to assist the Staff of the Commission (the “Staff”) in its review of the Registration Statement.

(1) Investment Objectives and Policies

The Fund seeks to maximize tax-free current income and terminate on or around December 2023.

The Fund seeks to achieve its investment objective by investing, under normal circumstances, at least 80% of its net assets in municipal bonds such that the interest on each bond is exempt from U.S. federal income taxes and the federal alternative minimum tax (“AMT”). Under normal circumstances, the Fund primarily invests in U.S. dollar denominated investment-grade fixed-rate municipal bonds, as well as money market instruments and registered investment companies. The Fund will invest in both callable and non-callable municipal bonds.

Under normal circumstances, the Fund’s effective duration will vary within one year (plus or minus) of the effective duration of the securities comprising the S&P AMT-Free Municipal Series Dec 2023 Index, as calculated by S&P Dow Jones Indices LLC, which as of                     , was          years. Effective duration is a measure of the Fund’s price sensitivity to changes in yields or interest rates; however, effective duration is not an exact measurement and may not reliably predict a particular security’s price sensitivity to changes in yield or interest rates. In addition, the Fund has the ability to invest in bonds that will mature at a later date than the Fund’s planned termination date.

The Fund will generally hold municipal bond securities issued by state and local municipalities whose interest payments are exempt from U.S. federal income tax, the federal AMT and the federal Medicare contribution tax of 3.8% on “net investment income,” including dividends, interest and capital gains. In the last months of operation, as the bonds held by the Fund mature, the proceeds will not be reinvested in bonds but instead will be held in cash and cash equivalents, including, without limitation, shares of BlackRock Cash Funds, AMT-free tax-exempt municipal notes, variable rate demand notes and obligations, tender option bonds and municipal commercial paper. In or around December 2023, the Fund will wind up and terminate, and its net assets will be distributed to then current shareholders.

The Fund is an actively managed exchange-traded fund that does not seek to replicate the performance of a specified index. The Fund may have a higher degree of portfolio turnover than funds that seek to replicate the performance of an index.

(2) Changes from Recent Filings

The Fund’s description of its investment strategy and risk factors are specific to this Fund. The portfolio managers are specific to this Fund.

The Amendment follows the general format used by previous Trust filings prepared in accordance with the revised Form N-1A, for example, Post-Effective Amendment No. 151 filed pursuant to Rule 485(a)(1) on March 4, 2015, relating to the iShares Interest Rate Hedged 10+ Year Credit Bond ETF, which became effective on June 8, 2015.

(3) Prior Filings with Similar Disclosure

Much of the disclosure in the Amendment is substantially similar to that in previous filings submitted by the Trust and reviewed by the Staff. In particular, we invite your attention to Post-Effective Amendment No. 151, filed pursuant to Rule 485(a)(1) on March 4, 2015.

In the Prospectus:

“Portfolio Holdings Information,” “Management – Investment Adviser,” “Management – Portfolio Managers,” “Management – Administrator, Custodian and Transfer Agent,” “Management – Conflicts of Interest,” “Shareholder Information – Book Entry,” “Shareholder Information – Share Prices,” “Shareholder Information – Determination of Net Asset Value,” “Shareholder Information – Creations and Redemptions,” “Shareholder Information – Costs Associated with Creations and Redemptions,” “Shareholder Information – Householding,” “Distribution,” “Financial Highlights,” and “Disclaimers.”

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In the Statement of Additional Information:

“Proxy Voting Policy,” “Portfolio Holdings Information,” “Continuous Offering,” “Investment Advisory, Administrative and Distribution Services – Portfolio Managers,” “Investment Advisory, Administrative and Distribution Services – Portfolio Manager Compensation Overview,” “Investment Advisory, Administrative and Distribution Services – Codes of Ethics,” “Investment Advisory, Administrative and Distribution Services – Anti-Money Laundering Requirements,” “Investment Advisory, Administrative and Distribution Services – Administrator, Custodian and Transfer Agent,” “Investment Advisory, Administrative and Distribution Services – Distributor,” “Investment Advisory, Administrative and Distribution Services – Payments by BFA and its Affiliates,” “Determination of Net Asset Value,” “Brokerage Transactions,” and “Financial Statements.”

*    *    *    *    *

The operations of the Fund, the description of the shares offered and the other information that is typically common in a fund complex do not appear to raise novel issues or problem areas that warrant particular attention of the Staff in reviewing the Registration Statement. Consequently, on behalf of the Trust, we request that the Registration Statement be given selective review by the Staff.¹

If you have any questions or need further information, please call me at (202) 303-1124.

Sincerely,

/s/ Benjamin J. Haskin

Benjamin J. Haskin

cc: Deepa Damre, Esq.

Marisa Rolland, Esq.

Katherine Drury

Michael Gung

Seong Kim

¹  See Inv. Co. Act Release No. 13768 (Feb. 15, 1984).

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