Kyrsten Lea Sinema (/ˈkɪərstən ˈsɪnəmə/ KEER-stən SIN-ə-mə; born July 12, 1976) is an American politician, lawyer, 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 became the first openly bisexual and the second openly LGBTQ woman (after Tammy Baldwin) to be elected to the Senate. Sinema also became 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 caucused with the Democrats.

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

Sinema was born in Tucson, Arizona, on July 12, 1976, to Marilyn (Wiley) and Dan Sinema. Sinema has an older brother and younger sister. Her father was an attorney. Her parents divorced when she was a child, and her mother, who had custody of the children, remarried. With her siblings, mother, and stepfather, Sinema moved to DeFuniak Springs, Florida, a small town on the Panhandle.

Sinema has said that when her stepfather lost his job and the bank foreclosed on their home, the family lived for three years in an abandoned gas station and that for two years they had no toilet or electricity while living there. She later recalled: "My stepdad built a bunkbed for me and my sister. We separated our bunkbed from the kitchen with one of those big chalkboards on rollers. I knew that was weird. A chalkboard shouldn't be a wall. A kitchen should have running water."

According to journalist Jonathan Martin in The New York Times, Sinema has given "contradictory answers about her early life," and her mother and stepfather have filed court documents saying they had made monthly payments for gas, electricity, and phone bills, even though Sinema had said they had been "without running water or electricity". Asked whether she had embellished details from her childhood, Sinema said, "I've shared what I remember from my childhood. I know what I lived through." Sinema was raised as a member of the Church of Jesus Christ of Latter-day Saints (LDS Church).

She graduated as valedictorian from Walton High School in DeFuniak Springs at age 16 and earned her B.A. from Brigham Young University (BYU) in 1995 at age 18. She left the LDS Church after graduating from BYU. Sinema returned to Arizona in 1995.