On May 20, 2026, AvalonBay Communities, Inc. (“AvalonBay”), Equity Residential (“Equity Residential”), ERP Operating Limited Partnership (“ERP Operating Partnership”) and Canopy Merger Sub LLC, a direct, wholly owned subsidiary of Equity Residential (“Merger Sub”), entered into an Agreement and Plan of Merger (as it may be amended from time to time, the “merger agreement”), which provides for the combination of Equity Residential and AvalonBay in a merger of equals transaction. Upon the terms and subject to the conditions set forth in the merger agreement, (i) on the closing date but prior to the effective time of the merger (the “effective time”), AvalonBay will contribute certain assets (the “asset contribution”) in exchange for units of partnership interest in ERP Operating Partnership that have, in the aggregate, a value equal to the fair market value of such contributed assets and (ii) following the asset contribution and at the effective time, AvalonBay will merge with and into Merger Sub, with Merger Sub surviving as a direct, wholly owned subsidiary of Equity Residential (the “merger”).

On behalf of the board of trustees of Equity Residential and board of directors of AvalonBay, we are pleased to enclose the accompanying joint proxy statement/prospectus relating to the merger. We are requesting that you take certain actions as a shareholder of Equity Residential or stockholder of AvalonBay, as applicable, as more fully described in this joint proxy statement/prospectus.

The merger agreement provides each share of common stock, par value $0.01 per share, of AvalonBay (“AvalonBay common stock”), issued and outstanding immediately prior to the effective time (other than certain excluded shares as further described in the merger agreement) will be converted into the right to receive 2.793 common shares of beneficial interest, par value $0.01 per share, of Equity Residential (“Equity Residential common shares”) and cash in lieu of fractional shares, if any.

The merger consideration is fixed and will not be adjusted to reflect stock price changes prior to the consummation of the merger. Equity Residential shareholders will continue to own their existing Equity Residential common shares, the form of which will not be changed by the transaction.

Upon completion of the merger, Equity Residential shareholders are expected to own approximately [ ]% of the combined company and former AvalonBay stockholders are expected to own the remaining [ ]%, based on the merger consideration and the number of shares and stock-based awards of Equity Residential and AvalonBay outstanding, in each case, as of [ ], 2026, the last practicable trading day before the date of the joint proxy statement/prospectus.

Each of the board of trustees of Equity Residential and the board of directors of AvalonBay (the “Equity Residential board” and “AvalonBay board,” respectively) has unanimously approved or adopted, as applicable, the merger agreement and the transactions contemplated by the merger agreement, including the merger and the share issuance.

The value of the merger consideration to be received in exchange for each share of AvalonBay common stock will fluctuate with the market value of Equity Residential common shares until the merger is completed.

Based on Equity Residential’s closing stock price on [ ], 2026, the last practicable trading day before the date of this joint proxy statement/prospectus, the implied value of the merger consideration was $[ ]. The Equity Residential common shares are listed on the New York Stock Exchange (“NYSE”) under the ticker symbol “EQR,” and AvalonBay common stock is listed on the NYSE under the ticker symbol “AVB.” We urge you to obtain current market quotations for the Equity Residential common shares and AvalonBay common stock.

Each of Equity Residential and AvalonBay will hold a special meeting of its shareholders or stockholders, respectively, in connection with the transactions contemplated by the merger agreement.

Equity Residential’s special meeting of shareholders (the “Equity Residential special meeting”) will be held virtually on [   ], 2026 at [   ] Central Time (unless it is adjourned or postponed to a later date) via live audio webcast at www.virtualshareholdermeeting.com/EQR2026SM. The Equity Residential special meeting will be held exclusively online via live audio webcast. At the Equity Residential special meeting, Equity Residential shareholders will be asked to consider and vote on the following matters: (i) a proposal to approve the issuance of Equity Residential common shares in connection with the merger (the “Equity Residential share issuance proposal”); (ii) a proposal to approve an amendment to the Declaration of Trust of Equity Residential to increase the number of authorized Equity Residential common shares (such amendment, the “Equity Residential charter amendment,” and such proposal, the “Equity Residential charter amendment proposal”); and (iii) a proposal to adjourn the Equity Residential special meeting from time to time, if necessary or appropriate, to solicit additional proxies in the event there are not sufficient votes at the time of the Equity Residential special meeting to approve the Equity Residential share issuance proposal (the “Equity Residential adjournment proposal”). The Equity Residential board has unanimously approved the merger agreement and the transactions contemplated by the merger agreement, including the merger and the share issuance, and unanimously recommends that Equity Residential shareholders vote “FOR” the Equity Residential share issuance proposal, “FOR” the Equity Residential charter amendment proposal, and “FOR” the Equity Residential adjournment proposal.

AvalonBay’s special meeting of stockholders (the “AvalonBay special meeting”) will be held virtually on [   ], 2026 at [   ] Eastern Time (unless it is adjourned or postponed to a later date) via live audio webcast at www.virtualshareholdermeeting.com/AVB2026SM. The AvalonBay special meeting will be held exclusively online via live audio webcast. At the AvalonBay special meeting, AvalonBay stockholders will be asked to consider and vote on the following matters: (i) a proposal to approve the merger and the other transactions contemplated by the merger agreement (the “AvalonBay merger proposal”); (ii) a proposal to approve, on a non-binding, advisory basis, the compensation that may be paid or become payable to the named executive officers of AvalonBay in connection with the transactions contemplated by the merger agreement (the “AvalonBay merger-related compensation proposal”); and (iii) a proposal to adjourn the AvalonBay special meeting from time to time, if necessary or appropriate, to solicit additional proxies in the event there are not sufficient votes at the time of the AvalonBay special meeting to approve the AvalonBay merger proposal (the “AvalonBay adjournment proposal”). The AvalonBay board has unanimously adopted the merger agreement and approved the transactions contemplated by the merger agreement, including the merger, and unanimously recommends that AvalonBay stockholders vote “FOR” the AvalonBay merger proposal, “FOR” the AvalonBay merger-related compensation proposal, and “FOR” the AvalonBay adjournment proposal.

The accompanying joint proxy statement/prospectus contains detailed information about Equity Residential, AvalonBay, the merger agreement, and the transactions contemplated by the merger agreement. In particular, see “Risk Factors” beginning on page 43. A copy of the merger agreement and a copy of the Equity Residential charter amendment are attached as Annex A and Annex B, respectively, to the accompanying joint proxy statement/prospectus, and each is incorporated by reference herein. We encourage you to read the accompanying joint proxy statement/prospectus and its annexes, including the merger agreement, carefully and in their entirety. You may also obtain information about Equity Residential and AvalonBay from the Securities and Exchange Commission (the “SEC”).

Your vote is very important regardless of the number of Equity Residential common shares or the number of shares of AvalonBay common stock that you own. The merger cannot be completed unless Equity Residential shareholders approve the issuance of Equity Residential common shares pursuant to the merger agreement and AvalonBay stockholders approve the merger.

Whether or not you plan to attend your company’s special meeting, please submit your proxy as soon as possible to make sure that your shares are represented at that meeting.

Neither the SEC nor any state securities commission has approved or disapproved of the merger or the other transactions described in this joint proxy statement/prospectus or the securities to be issued in connection with the merger or determined if this joint proxy statement/prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

This joint proxy statement/prospectus is dated [   ], 2026 and is first being mailed to shareholders of Equity Residential and stockholders of AvalonBay on or about [   ], 2026.

On May 20, 2026, AvalonBay Communities, Inc. (“AvalonBay”), Equity Residential (“Equity Residential”), ERP Operating Limited Partnership (“ERP Operating Partnership”) and Canopy Merger Sub LLC, a direct, wholly owned subsidiary of Equity Residential (“Merger Sub”), entered into an Agreement and Plan of Merger (as it may be amended from time to time, the “merger agreement”), which provides for the combination of Equity Residential and AvalonBay in a merger of equals transaction. Upon the terms and subject to the conditions set forth in the merger agreement (i) on the closing date but prior to the effective time of the merger (the “effective time”), AvalonBay will contribute certain assets (the “asset contribution”) in exchange for units of partnership interest in ERP Operating Partnership that have, in the aggregate, a value equal to the fair market value of such contributed assets and (ii) following the asset contribution and at the effective time, AvalonBay will merge with and into Merger Sub, with Merger Sub surviving as a direct, wholly owned subsidiary of Equity Residential (the “merger”).

NOTICE IS HEREBY GIVEN that a special meeting of Equity Residential shareholders (the “Equity Residential special meeting”) will be held virtually at [ ] Central Time, on [    ], 2026 (unless it is adjourned or postponed to a later date) via live audio webcast at www.virtualshareholdermeeting.com/EQR2026SM. The Equity Residential special meeting will be held exclusively online via live audio webcast.

We are pleased to notify you of, and invite you to attend, the Equity Residential special meeting. At the Equity Residential special meeting, holders of common shares of beneficial interest of Equity Residential (“Equity Residential shareholders”) will be asked to consider and vote on the following matters:

Approval of the Equity Residential share issuance proposal is required to complete the transactions contemplated by the merger agreement.

Equity Residential will transact no other business at the Equity Residential special meeting, except for business properly brought before the Equity Residential special meeting or any adjournment or postponement thereof by or at the direction of the Equity Residential board of trustees (the “Equity Residential board”). The accompanying joint proxy statement/prospectus describes the matters to be considered at the Equity Residential special meeting in more detail.

The Equity Residential board has set [    ], 2026 as the record date for the Equity Residential special meeting for determining the Equity Residential shareholders entitled to notice of and to vote at the Equity Residential special meeting and any adjournment or postponement thereof (the “Equity Residential record date”). Only Equity Residential shareholders of record at the close of business on [    ], 2026 are entitled to notice of, and to vote at, the Equity Residential special meeting. Holders of preferred shares of beneficial interest of Equity Residential are entitled to notice of the special meeting, and may attend the special meeting virtually by accessing the meeting website as guests, but may not vote or ask questions at the special meeting.

The Equity Residential special meeting will be held in a virtual format via audio webcast only. You will not be able to attend the meeting physically in person. To attend the Equity Residential special meeting, you must be a shareholder on the Equity Residential record date. To submit your proxy through the internet, you may vote your shares at www.proxyvote.com. You will need the 16-digit control number found on your proxy card or voting instruction form. Beneficial shareholders who do not have a control number should follow the instructions provided on the voting instruction form provided by your bank, broker, nominee, trustee or other record holder. Beneficial holders that wish to vote at the meeting must obtain a legal proxy from their bank, broker, nominee, trustee or other record holder prior to the meeting. You may need to have an electronic image (such as a .pdf file or scan) of the legal proxy with you if you are voting at the meeting.

Your vote is very important regardless of the number of Equity Residential common shares that you own. The transactions contemplated by the merger agreement cannot be completed without approval of the Equity Residential share issuance proposal by the affirmative vote of a majority of the votes cast by the holders of outstanding Equity Residential common shares represented in person or by proxy and entitled to vote on such matter at the Equity Residential special meeting, or any adjournment or postponement thereof. Whether or not you expect to participate in the Equity Residential special meeting, Equity Residential urges you to submit a proxy to have your shares voted as promptly as possible either: (i) via the internet on the website shown on the enclosed proxy card (see proxy card for instructions); (ii) by telephone (see proxy card for instructions); or (iii) by completing, signing, dating, and returning the enclosed proxy card in the postage-paid envelope provided, so that your shares may be represented and voted at the Equity Residential special meeting. If your shares are held in “street name” by a bank, broker, nominee, trustee or other record holder, please follow the instructions on the enclosed voting instruction card furnished by such bank, broker, nominee, trustee or other record holder.

The Equity Residential board has unanimously approved the merger agreement and the transactions contemplated by the merger agreement, including the merger and the share issuance, and unanimously recommends that you vote “FOR” the Equity Residential share issuance proposal, “FOR” the Equity Residential charter amendment proposal, and “FOR” the Equity Residential adjournment proposal.

The joint proxy statement/prospectus of which this notice is a part provides a detailed description of the merger agreement, the transactions contemplated thereby, including the merger, and the other matters to be considered at the Equity Residential special meeting. A summary of the merger agreement is included in the joint proxy statement/prospectus in the sections entitled “The Merger” and “The Merger Agreement,” a copy of the merger agreement is attached as Annex A to the joint proxy statement/prospectus and a copy of the Equity Residential charter amendment is attached as Annex B to the joint proxy statement/prospectus, each of which are incorporated by reference into this notice to the same extent as if fully set forth herein. We encourage you to carefully read this joint proxy statement/prospectus (including the annexes thereto) and any other documents incorporated by reference herein in their entirety.

PLEASE VOTE YOUR SHARES PROMPTLY. YOU CAN FIND INSTRUCTIONS FOR VOTING ON THE ENCLOSED PROXY CARD. IF YOUR SHARES ARE HELD IN “STREET” NAME BY A BANK, BROKER, NOMINEE, TRUSTEE OR OTHER RECORD HOLDER, PLEASE FOLLOW THE INSTRUCTIONS ON THE VOTING INSTRUCTION CARD FURNISHED BY SUCH BANK, BROKER, NOMINEE, TRUSTEE OR OTHER RECORD HOLDER. IF YOU HAVE QUESTIONS ABOUT THE MERGER, THE EQUITY RESIDENTIAL SHARE ISSUANCE PROPOSAL, THE EQUITY RESIDENTIAL CHARTER AMENDMENT PROPOSAL, THE EQUITY RESIDENTIAL ADJOURNMENT PROPOSAL OR VOTING YOUR SHARES, PLEASE CONTACT:

On May 20, 2026, Equity Residential, ERP Operating Limited Partnership (“ERP Operating Partnership”), Canopy Merger Sub LLC, a direct, wholly owned subsidiary of Equity Residential (“Merger Sub”), and AvalonBay Communities, Inc. (“AvalonBay”) entered into an Agreement and Plan of Merger (as it may be amended from time to time, the “merger agreement”), which provides for the combination of Equity Residential and AvalonBay in a merger of equals transaction. Upon the terms and subject to the conditions set forth in the merger agreement, (i) on the closing date but prior to the effective time of the merger (the “effective time”), AvalonBay will contribute certain assets (the “asset contribution”) in exchange for units of partnership interest in ERP Operating Partnership that have, in the aggregate, a value equal to the fair market value of such contributed assets and (ii) following the asset contribution and at the effective time, AvalonBay will merge with and into Merger Sub, with Merger Sub surviving as a direct, wholly owned subsidiary of Equity Residential (the “merger”).

NOTICE IS HEREBY GIVEN that a special meeting of stockholders of AvalonBay (the “AvalonBay special meeting”) will be held virtually at [    ] Eastern Time, on [    ], 2026 (unless it is adjourned or postponed to a later date) via live audio webcast at www.virtualshareholdermeeting.com/AVB2026SM. The AvalonBay special meeting will be held exclusively online via live audio webcast.

We are pleased to notify you of, and invite you to attend, the AvalonBay special meeting. At the AvalonBay special meeting, holders of common stock of AvalonBay (“AvalonBay common stockholders”) will be asked to consider and vote on the following matters:

Approval of the AvalonBay merger proposal is required to complete the transactions contemplated by the merger agreement.

AvalonBay will transact no other business at the AvalonBay special meeting, except for business properly brought before the AvalonBay special meeting or any adjournment or postponement thereof by or at the direction of the AvalonBay board of directors (the “AvalonBay board”). The accompanying joint proxy statement/prospectus describes the matters to be considered at the AvalonBay special meeting in more detail. The AvalonBay board has set [    ], 2026 as the record date for the AvalonBay special meeting for determining the AvalonBay common stockholders entitled to notice of, and to vote at, the AvalonBay special meeting and any adjournment or postponement thereof (the “AvalonBay record date”). Only AvalonBay common stockholders of record at the close of business on [    ], 2026 are entitled to notice of, and to vote at, the AvalonBay special meeting.

The AvalonBay special meeting will be held in a virtual format via audio webcast only. You will not be able to attend the meeting physically in person. To attend the AvalonBay special meeting, you must be a stockholder on the AvalonBay record date. To submit your proxy through the internet, you may vote your shares at www.proxyvote.com. You will need the 16-digit control number found on your proxy card or voting instruction form. Beneficial stockholders who do not have a control number should follow the instructions provided on the voting instruction form provided by your bank, broker, nominee, trustee or other record holder. Beneficial holders that wish to vote at the meeting must obtain a legal proxy from their bank, broker, nominee, trustee or other record holder prior to the meeting. You may need to have an electronic image (such as a .pdf file or scan) of the legal proxy with you if you are voting at the meeting.

Your vote is very important regardless of the number of shares of AvalonBay common stock that you own. The transactions contemplated by the merger agreement cannot be completed without approval of the AvalonBay merger proposal by the affirmative vote of the holders of at least a majority of the outstanding shares of AvalonBay common stock entitled to vote at the AvalonBay special meeting. Whether or not you expect to participate in the AvalonBay special meeting, AvalonBay urges you to submit a proxy to have your shares voted as promptly as possible either: (i) via the internet on the website shown on the enclosed proxy card (see proxy card for instructions); (ii) by telephone (see proxy card for instructions); or (iii) by completing, signing, dating, and returning the enclosed proxy card in the postage-paid envelope provided, so that your shares may be represented and voted at the AvalonBay special meeting. If your shares are held in “street name” by a bank, broker, nominee, trustee or other record holder, please follow the instructions on the enclosed voting instruction card furnished by such bank, broker, nominee, trustee or other record holder.

The AvalonBay board has unanimously approved the merger agreement and the transactions contemplated by the merger agreement, including the merger, and unanimously recommends that you vote “FOR” the AvalonBay merger proposal, “FOR” the AvalonBay merger-related compensation proposal, and “FOR” the AvalonBay adjournment proposal.

The joint proxy statement/prospectus of which this notice is a part provides a detailed description of the merger agreement, the transactions contemplated thereby, including the merger, and the other matters to be considered at the AvalonBay special meeting. A summary of the merger agreement is included in the joint proxy statement/prospectus in the sections entitled “The Merger” and “The Merger Agreement,” and a copy of the merger agreement is attached as Annex A to the joint proxy statement/prospectus, each of which are incorporated by reference into this notice to the same extent as if fully set forth herein. We encourage you to carefully read this joint proxy statement/prospectus (including the annexes thereto) and any other documents incorporated by reference herein in their entirety.

PLEASE VOTE YOUR SHARES PROMPTLY. YOU CAN FIND INSTRUCTIONS FOR VOTING ON THE ENCLOSED PROXY CARD. IF YOUR SHARES ARE HELD IN “STREET NAME” BY A BANK, BROKER, NOMINEE, TRUSTEE OR OTHER RECORD HOLDER, PLEASE FOLLOW THE INSTRUCTIONS ON THE VOTING INSTRUCTION CARD FURNISHED BY SUCH BANK, BROKER, NOMINEE, TRUSTEE OR OTHER RECORD HOLDER. IF YOU HAVE QUESTIONS ABOUT THE MERGER, THE MERGER PROPOSAL, THE MERGER-RELATED COMPENSATION PROPOSAL, THE AVALONBAY ADJOURNMENT PROPOSAL, OR VOTING YOUR SHARES, PLEASE CONTACT:

This joint proxy statement/prospectus incorporates by reference important business and financial information about Equity Residential (“Equity Residential”) and AvalonBay Communities, Inc. (“AvalonBay”) from other documents that are not included in or delivered with this joint proxy statement/prospectus. For a listing of the documents incorporated by reference into this joint proxy statement/prospectus and additional information, see “Where You Can Find More Information.”

You can obtain any of the documents incorporated by reference into this joint proxy statement/prospectus without charge by requesting them in writing or by telephone from MacKenzie Partners, Inc., Equity Residential’s proxy solicitor, or Innisfree M&A Incorporated, AvalonBay’s proxy solicitor, at the following addresses and telephone numbers:

You will not be charged for any of these documents that you request. To receive timely delivery of the documents in advance of the special meetings, you should make your request no later than [    ], 2026, which is five (5) business days before the special meetings.

You may also obtain any of the documents incorporated by reference into this joint proxy statement/prospectus without charge through the Securities and Exchange Commission (the “SEC”) website at www.sec.gov. In addition, you may obtain copies of documents filed by Equity Residential with the SEC by accessing “Filings – SEC Filings” in the “Investor” section of Equity Residential’s website at www.equityapartments.com. You may also obtain copies of documents filed by AvalonBay with the SEC by accessing the “Investors” section of AvalonBay’s website at www.avalonbay.com.

We are not incorporating the contents of the websites of the SEC, Equity Residential, AvalonBay or any other entity into this joint proxy statement/prospectus. We are providing the information about how you can obtain certain documents that are incorporated by reference into this joint proxy statement/prospectus at these websites only for your convenience.

Except where the context otherwise states, Equity Residential has supplied all information contained in or incorporated by reference into this joint proxy statement/prospectus relating to Equity Residential (including the annexes hereto), and AvalonBay has supplied all information contained in or incorporated by reference into this joint proxy statement/prospectus relating to AvalonBay (including the annexes hereto). Equity Residential and AvalonBay both contributed information relating to the merger.

This joint proxy statement/prospectus forms a part of a registration statement on Form S-4 (Registration No. 333-[ ]) filed by Equity Residential with the SEC. It constitutes a prospectus of Equity Residential under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), and the rules thereunder, with respect to the Equity Residential common shares of beneficial interest, par value $0.01 per share (the “Equity Residential common shares”), to be issued to AvalonBay stockholders pursuant to the Agreement and Plan of Merger (the “merger agreement”), dated May 20, 2026, by and among AvalonBay, Equity Residential, ERP Operating Limited Partnership (“ERP Operating Partnership”) and Canopy Merger Sub LLC (“Merger Sub”). Upon the terms and subject to the conditions set forth in the merger agreement, (i) on the closing date but prior to the effective time of the merger (the “effective time”), AvalonBay will contribute certain assets (the “asset contribution”) in exchange for units of partnership interest in ERP Operating Partnership that have, in the aggregate, a value equal to the fair market value of such contributed assets and (ii) following the asset contribution and at the effective time, AvalonBay will merge with and into Merger Sub, with Merger Sub surviving as a direct, wholly owned subsidiary of Equity Residential (the “merger”). This joint proxy statement/prospectus also constitutes a proxy statement under Section 14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and a notice of meeting (x) with respect to the Equity Residential special meeting at which Equity Residential shareholders will consider and vote on the Equity Residential share issuance proposal, the Equity Residential charter amendment proposal, and the Equity Residential adjournment proposal, and (y) with respect to the AvalonBay special meeting at which AvalonBay stockholders will consider and vote on the AvalonBay merger proposal, the AvalonBay merger-related compensation proposal, and the AvalonBay adjournment proposal.

You should rely only on the information contained in or incorporated by reference into this joint proxy statement/prospectus (including the annexes hereto). No one has been authorized to provide you with information that is different from that contained in or incorporated by reference into this joint proxy statement/prospectus (including the annexes hereto). You should not assume that the information included as annexes or contained in any document incorporated by reference herein is accurate as of any date other than the date of such document. Any statement contained in a document incorporated or deemed to be incorporated by reference into this joint proxy statement/prospectus will be deemed to be modified or superseded to the extent that a statement contained herein or in any other subsequently filed document which also is, or is deemed to be, incorporated by reference into this joint proxy statement/prospectus modifies or supersedes that statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this joint proxy statement/prospectus. Neither Equity Residential nor AvalonBay assumes any obligation to update the information contained in this joint proxy statement/prospectus (whether as a result of new information, future events, or otherwise), except as required by applicable law. Neither the mailing of this joint proxy statement/prospectus to the shareholders of Equity Residential or stockholders of AvalonBay, nor Equity Residential or AvalonBay taking any actions contemplated hereby at any time, will create any implication to the contrary.

This joint proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction in which or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction.

The following questions and answers are intended to briefly address some commonly asked questions regarding the Equity Residential and AvalonBay special meetings, the merger agreement, the merger, the share issuance, and the other transactions contemplated by the merger agreement. Equity Residential and AvalonBay urge you to carefully read this entire joint proxy statement/prospectus, including the annexes and the other documents referred to or incorporated by reference into this joint proxy statement/prospectus, because the information in this section does not provide all of the information that might be important to you.

On May 20, 2026, AvalonBay, Equity Residential, ERP Operating Partnership and Merger Sub entered into the merger agreement to combine through a stock-for-stock merger and form the combined company. Upon the terms and subject to the conditions of the merger agreement, (i) on the closing date but prior to the effective time, AvalonBay will contribute certain assets in exchange for ERP Operating Partnership units that have, in the aggregate, a value equal to the fair market value of such contributed assets and (ii) following the asset contribution and at the effective time, AvalonBay will merge with and into Merger Sub, with Merger Sub surviving the merger as a direct, wholly owned subsidiary of Equity Residential. A summary of the merger agreement is included in this joint proxy statement/prospectus in the sections entitled “The Merger” and “The Merger Agreement,” and a copy of the merger agreement is attached as Annex A hereto. You are urged to read this joint proxy statement/prospectus, the merger agreement and any other documents incorporated by reference herein in their entirety.

The merger agreement provides that each share of AvalonBay common stock (other than shares of AvalonBay common stock held in treasury or held or owned by AvalonBay, Equity Residential or Merger Sub (collectively, the “cancelled shares”)) issued and outstanding immediately prior to the merger will be converted at the effective time into the right to receive 2.793 Equity Residential common shares and cash in lieu of fractional shares, if any. This exchange ratio is fixed and will not be adjusted to reflect stock price changes prior to the consummation of the merger. Accordingly, the value of the consideration to be received in exchange for each share of AvalonBay common stock will fluctuate with the market value of Equity Residential common shares until the merger is completed.

Equity Residential and AvalonBay expect to complete the merger in the second half of 2026, although Equity Residential and AvalonBay cannot assure completion by any particular date, if at all.

Immediately following the completion of the merger, former AvalonBay stockholders are expected to own approximately 51.2% and legacy Equity Residential shareholders approximately 48.8% of the then outstanding Equity Residential common shares, as of the date of the execution of the merger agreement. After consideration of all applicable factors pursuant to the business combination accounting rules, the merger results in a reverse acquisition in which Equity Residential is considered the “legal acquirer” because Equity Residential issues Equity Residential common shares to AvalonBay stockholders, while AvalonBay is the “accounting acquirer” based on the following indicators: (i) former AvalonBay stockholders will hold the largest portion of the voting rights in the combined company; and (ii) AvalonBay’s senior management, including its Chief Executive Officer and President, will comprise the majority of the executive management team of the combined company. Although Equity Residential is issuing Equity Residential common shares to AvalonBay stockholders for legal purposes, AvalonBay is treated as the buyer for accounting purposes with Equity Residential treated as the acquiree. Accordingly, the following Unaudited Pro Forma Condensed Consolidated Financial Statements present AvalonBay’s historical balances and results, with Equity Residential’s assets and liabilities recorded at estimated fair value.

On May 20, 2026, in connection with the merger, ERP Operating Partnership entered into the Commitment Letter with MSSF, Wells Fargo Securities, LLC and Wells Fargo Bank, pursuant to which MSSF (and its designated affiliates) and Wells Fargo Bank have committed to provide ERP Operating Partnership with the Bridge Facility. The proceeds of the Bridge Facility, together with cash on hand and proceeds of commercial paper issuances, are expected to be available to fund any repayment or refinancing of ERP Operating Partnership’s existing indebtedness and AvalonBay’s existing indebtedness and to pay fees and expenses related to the merger, subject to the satisfaction of customary conditions set forth in the Commitment Letter. The Bridge Facility has a maximum commitment amount of $2.0 billion, is expected to initially bear interest on amounts drawn at a rate of SOFR + 0.725% per annum (subject to change based on credit ratings and the time the Bridge Facility remains outstanding) plus additional fees, and will mature 364 days following the closing of the merger. The timing and amounts of borrowings under the Bridge Facility, if any, have not yet been determined. Therefore, the pro forma financial information does not give effect to the Bridge Facility. However, the pro forma financial information gives effect to the expected issuance of commercial paper to finance estimated transaction costs that will be incurred for the merger.

The accompanying Unaudited Pro Forma Condensed Consolidated Balance Sheet as of March 31, 2026 has been prepared as if the merger had occurred as of that date. The accompanying Unaudited Pro Forma Condensed Consolidated Statements of Operations for the year ended December 31, 2025 and for the three months ended March 31, 2026 have been prepared as if the merger had occurred on January 1, 2025.

Pro forma adjustments, and the assumptions on which they are based, are described in the accompanying “Notes to Unaudited Pro Forma Condensed Consolidated Financial Statements.” The pro forma adjustments and the preliminary fair value measurements as presented are based on estimates and certain information that is currently available. The total deemed consideration (calculated based on the fair value of shares of AvalonBay common stock as if AvalonBay had issued AvalonBay common stock to effect the merger) and the assignment of fair values to Equity Residential’s identifiable assets acquired and liabilities assumed are preliminary and based upon currently available information and certain assumptions, are subject to change and could vary materially from the actual amounts at the time the merger is completed. The fair value allocation will be finalized subsequent to the merger being consummated.

The pro forma information has been prepared in accordance with Article 11 of Regulation S-X as promulgated by the SEC, as amended by the SEC’s final rule, Release No. 33-10786, “Amendments to Financial Disclosures about Acquired and Disposed Businesses.” All significant adjustments necessary to reflect the effects of the merger are based on reasonable estimates using the information currently available. The pro forma information is presented for illustrative purposes only and is not necessarily indicative of the combined operating results or financial position that would have occurred if such transactions had been consummated on the dates and in accordance with the assumptions described herein, nor is it necessarily indicative of future operating results or financial position of the combined company.

The Unaudited Pro Forma Condensed Consolidated Financial Statements, although helpful in illustrating the financial position and results of operations of the combined company under one set of assumptions, do not reflect the benefits of expected cost savings (or associated costs to achieve such savings), opportunities to earn additional revenue and any costs necessary to earn additional revenue, or other factors that may result as a consequence of the merger and do not attempt to predict or suggest future results.

You are urged to read the pro forma information below together with the historical audited and unaudited consolidated financial statements of each of AvalonBay and Equity Residential and the related notes thereto, each of which is incorporated by reference into this joint proxy statement/prospectus. See “Where You Can Find More Information” for the location of information incorporated by reference into this joint proxy statement/prospectus.