The 117th United States Congress was a meeting of the legislative branch of the United States federal government, composed of the United States Senate and the United States House of Representatives. It convened in Washington, D.C., on January 3, 2021, during the final weeks of Donald Trump's presidency and the first two years of Joe Biden's presidency and ended on January 3, 2023.
 The 2020 elections decided control of both chambers. In the House of Representatives, the Democratic Party retained their majority, albeit reduced from the 116th Congress. It was similar in size to the majority held by the Republican Party during the 83rd Congress (1953–1955).
 In the Senate, Republicans briefly held the majority at the start; however, on January 20, 2021, three new Democratic senators – Jon Ossoff and Raphael Warnock of Georgia and Alex Padilla of California – were sworn in, resulting in 50 seats held by Republicans, 48 seats held by Democrats, and two held by independents who caucus with the Democrats. Effectively, this created a 50–50 split, which had not occurred since the 107th Congress in 2001. This was only the fourth time in U.S. history that the Senate has been evenly split—the first being in the 47th Congress (1881–1883)—and the longest lasting one ever.
 The new senators were sworn into office by Vice President Kamala Harris, just hours after her inauguration. With Harris serving as the tie breaker in her constitutional role as President of the Senate, Democrats gained control of the Senate, and thereby full control of Congress for the first time since the 111th Congress ended in 2011. Additionally, with the inauguration of Joe Biden as president that same day, Democrats assumed control of the executive branch as well, attaining an overall federal government trifecta, also for the first time since the 111th Congress.
 Despite Democrats holding thin majorities in both chambers during a period of intense political polarization, the 117th Congress oversaw the passage of numerous significant bills, including the Inflation Reduction Act, American Rescue Plan, Infrastructure Investment and Jobs Act, Postal Service Reform Act, Bipartisan Safer Communities Act, CHIPS and Science Act, Honoring Our PACT Act, Electoral Count Reform and Presidential Transition Improvement Act, and Respect for Marriage Act.
 Note: Democrats refer to themselves as a "caucus"; Republicans refer to themselves as a "conference".
 (minority until January 20, 2021, majority thereafter)
 (majority until January 20, 2021, minority thereafter)
 The numbers refer to their Senate classes. All class 1 senators are in the middle of their term (2019–2025), having been elected in 2018 and facing re-election in 2024. Class 2 senators are at the beginning of their term (2021–2027), having been elected in 2020 and facing re-election in 2026. Class 3 senators are at the end of their term (2017–2023), having been elected in 2016 and facing re-election in 2022.
 
 
  
 All 435 seats for voting members, along with the six non-voting delegates were filled by election in November 2020.
 
 
  
 Section contents: Senate, House, Joint
 Prior to the passing of an organizing resolution on February 3, 2021, chairs of Senate committees remained the same as in the 116th Congress. Where the chair had retired (as in the Agriculture, Budget, and HELP committees), the chair was vacant.