Exhibit 1.1

ERP OPERATING LIMITED PARTNERSHIP

(an Illinois limited partnership)

$500,000,000 3.00% Notes due 2023

TERMS AGREEMENT

Dated: April 3, 2013

c/o Equity Residential

Two North Riverside Plaza

Chicago, Illinois 60606

Attention: Mark Parrell

Ladies and Gentlemen:

We (the “Representatives”) understand that ERP Operating Limited Partnership, an Illinois limited partnership (“ERP”), proposes to issue and sell $500,000,000 aggregate principal amount of 3.00% Notes due 2023 (the “Underwritten Securities”). Subject to the terms and conditions set forth or incorporated by reference herein, the Underwriters named below (the “Underwriters”) severally, and not jointly, agree to purchase the respective amounts of the Underwritten Securities set forth below opposite their respective names, at the purchase price set forth below.

The Underwritten Securities shall have the following terms:

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All the provisions contained in the document attached as Annex A hereto entitled “ERP Operating Limited Partnership—Debt Securities—Standard Underwriting Provisions” dated April 3, 2013 (the “Standard Underwriting Provisions”) are hereby incorporated by reference in their entirety herein and shall be deemed to be a part of this Terms Agreement to the same extent as if such provisions had been set forth in full herein. Terms defined in such document are used herein as therein defined.

For purposes of this transaction, the term “Time of Sale” as used in the Standard Underwriting Provisions and this Terms Agreement shall mean 3:03 p.m. on the date hereof.

The Time of Sale Information for this transaction shall constitute the following: (1) any scheduled Issuer Free Writing Prospectuses attached as Annex B hereto, (2) the Preliminary Prospectus Supplement dated April 3, 2013, together with the Base Prospectus and (3) any filing under the 1934 Act which is deemed incorporated by reference in the Registration Statement, the Preliminary Prospectus Supplement or the Base Prospectus.

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This Agreement supersedes all prior agreements and understandings (whether written or oral) between ERP and the several Underwriters, or any of them, with respect to the offer and sale of the Underwritten Securities.

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Please accept this offer no later than 6:00 p.m. (New York City time) on April 3, 2013, by signing a copy of this Terms Agreement in the space set forth below and returning the signed copy to us.

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Annex A

ERP Operating Limited Partnership

Debt Securities

Standard Underwriting Provisions

Annex B

Issuer Free Writing Prospectus

PRICING TERM SHEET

3.00% Notes due 2023

Note: A securities rating is not a recommendation to buy, sell or hold securities and may be subject to revision or withdrawal at any time.

The issuer has filed a registration statement (including a prospectus) with the Securities and Exchange Commission (SEC) for the offering to which this communication relates. Before you invest, you should read the prospectus in that registration statement and other documents the issuer has filed with the SEC for more complete information about the issuer and this offering.

You may get these documents for free by visiting EDGAR on the SEC Web site at www.sec.gov. Alternatively, the issuer, any underwriter or any dealer participating in the offering will arrange to send you the prospectus if you request it by calling Citigroup Global Markets Inc., toll free at 1-800-831-9146 or by email at batprospectusdept@citi.com; by calling Barclays Capital Inc. at 1-888-603-5847 or by email at barclaysprospectus@broadridge.com; by calling Morgan Stanley & Co. LLC at 1-866-718-1649; or by calling RBC Capital Markets, LLC at 1-866-375-6829 or by email at usdebtcapitalmarkets@rbccm.com.

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