AMERICAN TOWER CORP /MA/

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Filed by the Registrantx Filed by a Party other than the Registrant ☐

Check the appropriate box:

Letter From the Chief Executive Officer

Dear Stockholder:

It is my pleasure to invite you to American Tower Corporation’s 2026 Annual Meeting of Stockholders on Wednesday, May 20, 2026 at 11:00 a.m. Eastern Time. We will hold the Annual Meeting virtually through a live audio webcast. You will be able to attend the meeting by visitingwww.virtualshareholdermeeting.com/AMT2026. Please follow the instructions in this Proxy Statement to join the virtual Annual Meeting.

Included with this letter are the official notice of meeting; the Proxy Statement, which describes in detail the matters to be discussed and voted on at the meeting; and the form of proxy.

Your vote is important. You may vote your shares online; by telephone; by mail, if you received a paper copy of the proxy materials and follow the instructions on the proxy card or voting instruction card; or at the virtual meeting. If you vote by proxy prior to the meeting, you may withdraw your proxy and vote at the virtual meeting, if you wish to do so. Whether or not you plan to attend the meeting, I urge you to vote as soon as possible to ensure your shares will be represented at the meeting.

On behalf of the executive team and your Board of Directors, I thank you for your continued support.

Sincerely,

Steven O. Vondran

President and Chief Executive Officer

Letter From the Independent Chairperson of the Board

Dear Fellow Stockholders:

It is a privilege to serve as Chairperson of the Board at American Tower. On behalf of the Board, I thank our stockholders for their continued trust as we oversee the Company’s strategy and long‑term value creation.

Throughout 2025, the Board and management remained focused on supporting long‑term stockholder value bydriving sustainable revenue growth, enhancing operational efficiency, andmaintaining a disciplined capital allocation strategy.

Revenue growth in 2025 reflected the essential nature of our global tower and data center portfolio alongside rapid growth in data consumption. At the same time, management advanced initiatives to strengthen operating discipline, reinforce the scalability and predictability of the business, and deliver margin improvement. We globalized our finance and operations functions, driving process optimization and an increased focus on leveraging AI applications. The Board continued to oversee a balanced capital allocation framework, focused primarily on developed markets, to deliver reliable, high‑quality financial results through a range of market conditions.

Engagement with our investors continues to be a vital part of the Board’s oversight. During 2025, we maintained an active dialogue with stockholders on strategy, governance, executive compensation, and Board composition. These conversations provide valuable perspective and help ensure our governance practices remain aligned with stockholder expectations and long‑term interests.

Board refreshment and succession planning also remained key areas of focus. In August 2025, we welcomed Gene Reilly to the Board, who brings over 30 years of experience overseeing operations and strategy at a fellow REIT company, further strengthening the range of skills and experience supporting our oversight of the Company’s strategy. This addition reflects our ongoing commitment to thoughtful refreshment.

As further evidence of our disciplined approach to Board refreshment, over the past several years we have welcomed six new independent directors whose varied and complementary experiences have brought fresh perspectives to the Board as we advance the Company’s strategic priorities. During this same period, six directors have rotated off the Board, including Bob Hormats, who will not be standing for re‑election at this year’s Annual Meeting. We are deeply grateful to Bob for his many years of service and for the invaluable perspective he provided on public policy and international strategy.

Looking ahead to 2026, we expect our integrated portfolio of towers and data centers to increasingly place American Tower at the heart of the global digital infrastructure ecosystem. We believe our differentiated global scale, long-standing customer partnerships and financial strength position us well to benefit from accelerating demand across wireless, cloud, and AI while remaining focused on execution, capital allocation, and value creation for stockholders.

Thank you for your continued confidence in American Tower. Serving on behalf of our stockholders is a responsibility the Board and I take seriously, and we remain committed to overseeing a strategy that supports durable growth and long‑term success.

Sincerely,

Pamela D. A. Reeve

Independent Chairperson of the Board

Special Note About Forward-Looking Statements

In addition to historical information, this Proxy Statement contains “forward-looking statements” concerning our goals, beliefs, expectations, strategies, objectives, plans, future operating results and underlying assumptions and other statements that are not necessarily based on historical facts. Actual results may differ materially from those indicated in our forward-looking statements as a result of various factors, including those factors set forth under the caption “Risk Factors” in Item 1A of our most recent annual report on Form 10-K, and other risks described in documents we subsequently file from time to time with the Securities and Exchange Commission (SEC). We undertake no obligation to update the information contained in this Proxy Statement to reflect subsequently occurring events or circumstances.

No Incorporation By Reference

This Proxy Statement includes several website addresses and references to additional materials and reports found on those websites. We have included such website addresses only as inactive textual references and do not intend them to be active links to such websites. These websites, materials and reports are not incorporated by reference herein.

Notice of 2026 Annual Meeting of Stockholders

American Tower Corporation,

222 Berkeley Street, Boston,

Massachusetts 02116

AT THE ANNUAL MEETING YOU WILL BE ASKED TO:

Transact such other business as may properly come before the meeting or any adjournments or postponements thereof.

For more detailed information on voting, please see “How do I cast a vote?” in the “Questions & Answers” section beginning on page 93 of this Proxy Statement.

To sign up for electronic delivery, please visit www.proxyvote.com with your proxy card in hand, which contains your control number, and follow the instructions to indicate that you agree to receive or access proxy materials electronically in future years.

ATTENDING THE MEETING

We will hold the Annual Meeting virtually through a live audio webcast.

•You will be able to attend the Annual Meeting online through a live audio webcast at www.virtualshareholdermeeting.com/AMT2026. You may log in with your 16-digit control number, included on your notice of internet availability of the proxy materials, on your proxy card, or on the instructions that accompanied your proxy materials (if applicable). For more information, please see “How do I attend the Annual Meeting?” in the “Questions & Answers” section beginning on page 93 of this Proxy Statement.

•The Annual Meeting will begin at approximately 11:00 a.m. Eastern Time, with registration beginning at 10:30 a.m., on Wednesday, May 20, 2026.

•You will be able to vote and submit live questions during the Annual Meeting at www.virtualshareholdermeeting.com/AMT2026.

By order of the Board of Directors,

Ruth T. Dowling

Executive Vice President, Chief Administrative Officer, General Counsel and Secretary

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