Kyrsten Lea Sinema ( KEER-stən SIN-ə-mə; born July 12, 1976) is an American politician and former social worker who served from 2019 to 2025 as a United States senator from Arizona. A former member of the Democratic Party, Sinema became an independent in December 2022.

Sinema served three terms as a state representative for the 15th legislative district from 2005 to 2011, one term as the state senator for the 15th legislative district from 2011 to 2012, and three terms as the United States representative for the 9th district from 2013 to 2019. She began her political career in the Arizona Green Party and rose to prominence for her progressive advocacy, supporting causes such as LGBT rights and opposing the war on terror. She left the Green Party to join the Arizona Democratic Party in 2004 and was elected to a seat in the United States House of Representatives in 2012. After her election, she joined the New Democrat Coalition, the Blue Dog Coalition and the bipartisan Problem Solvers Caucus, amassing one of the most conservative voting records in the Democratic caucus.

Sinema won the 2018 Senate election to replace the retiring Jeff Flake, defeating Republican nominee Martha McSally. She is the first openly bisexual and the second openly LGBT woman (after Tammy Baldwin) to be elected to the Senate. Sinema is also the first woman elected to the Senate from Arizona and the only religiously unaffiliated member of the Senate. She was one of four independents in the Senate, alongside Bernie Sanders, Angus King, and Joe Manchin, all of whom caucus with the Democrats.

Sinema was considered a key swing vote in the Senate during the 117th and 118th Congresses, when it was almost split between Democrats and Republicans. On March 5, 2024, she announced she would not seek reelection. Democrat Ruben Gallego won her seat in the 2024 election.