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Table of Contents ( Mark One ) UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Delaware ( State or other jurisdiction of incorporation or organization ) FORM 10 - K 100 Summer Street , Suite 2300 Boston , Massachusetts ( Address of Principal Executive Offices ) Title of each class Class A Common Stock , $ 0.001 par value Commission File Number 001-34620 IRONWOOD PHARMACEUTICALS , INC . ( Exact name of registrant as specified in its charter ) Securities registered pursuant to Section 12 ( b ) of the Act : ( 617 ) 621-7722 ( Registrant's telephone number , including area code ) to Trading Symbol ( s ) IRWD 04-3404176 ( I.R.S. Employer Identification Number ) 02110 ( Zip Code ) Name of each exchange on which registered Nasdaq Global Select Market Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes > No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the Exchange Act . Yes No 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 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 ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the Registrant was required to submit and post such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a 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 . Large accelerated filer > Accelerated filer Non - accelerated filer Smaller reporting company Emerging growth 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 . > Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No Aggregate market value of voting stock held by non - affiliates of the Registrant as of June 30 , 2020 : $ 1,634,804,172 As of February 10 , 2021 , there were 160,962,175 shares of Class A Common Stock outstanding . DOCUMENTS INCORPORATED BY REFERENCE : Portions of the definitive proxy statement for our 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this report .