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Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ( Mark One ) : Annual report pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 . For the fiscal year ended December 31 , 2020 Transition report pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 . For the transition period from to Commission File Number : 001-14195 American Tower Corporation ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of Incorporation or Organization ) Title of each Class Common Stock , $ 0.01 par value 1.375 % Senior Notes due 2025 1.950 % Senior Notes due 2026 0.500 % Senior Notes due 2028 1.000 % Senior Notes due 2032 116 Huntington Avenue Boston , Massachusetts 02116 ( Address of principal executive offices ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) Telephone Number ( 617 ) 375-7500 ( Registrant's telephone number , including area code ) X 65-0723837 ( I.R.S. Employer Identification No. ) AMT AMT 25A AMT 26B AMT 28A AMT 32 0 0 Name of exchange on which registered New York Stock Exchange New York Stock Exchange Securities registered pursuant to Section 12 ( g ) of the Act : None Yes 区 No 区 Indicate by check mark if the registrant is a well known seasoned issuer , as defined in Rule 405 of the Securities Act : Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act : Yes Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days : Yes No □ New York Stock Exchange New York Stock Exchange New York Stock Exchange Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , smaller reporting company , or an emerging growth company . See the definitions of “ large accelerated filer , " " accelerated filer , " " smaller reporting company , ” and “ emerging growth company ” in Rule 12b - 2 of the Exchange Act . ( Check One ) : Large accelerated filer Non - accelerated filer Emerging growth company Accelerated filer Smaller reporting company ■ If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( §15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . 冈 No | Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) : Yes □ The aggregate market value of the voting and non - voting common stock held by non - affiliates of the registrant as of June 30 , 2020 was $ 114.3 billion , based on the closing price of the registrant's common stock as reported on the New York Stock Exchange as of the last business day of the registrant's most recently completed second quarter . As of February 18 , 2021 , there were 444,384,437 shares of common stock outstanding . DOCUMENTS INCORPORATED BY REFERENCE Portions of the definitive proxy statement ( the " Definitive Proxy Statement " ) to be filed with the Securities and Exchange Commission relative to the registrant's 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this Report .