2014 United States Senate elections

The 2014 United States Senate elections were held on November 4, 2014. A total of 36 seats in the 100-member U.S. Senate were contested. Thirty-three Class 2 seats were contested for regular six-year terms to be served from January 3, 2015, to January 3, 2021, and three Class 3 seats were contested in special elections due to Senate vacancies. The elections marked 100 years of direct elections of U.S. senators. Going into the elections, 21 of the contested seats were held by the Democratic Party, while 15 were held by the Republican Party.

The Republicans regained the majority of the Senate in the 114th Congress, which started in January 2015; the Republicans had not controlled the Senate since January 2007. They needed a net gain of at least six seats to obtain a majority and were projected by polls to do so. On election night, they held all of their seats and gained nine Democratic-held seats. Republicans defeated five Democratic incumbents: Mark Begich of Alaska lost to Dan Sullivan, Mark Pryor of Arkansas lost to Tom Cotton, Mark Udall of Colorado lost to Cory Gardner, Mary Landrieu of Louisiana lost to Bill Cassidy, and Kay Hagan of North Carolina lost to Thom Tillis. Republicans also picked up another four open seats in Iowa, Montana, South Dakota, and West Virginia that were previously held by Democrats. Democrats did not pick up any Republican-held seats, but they did hold an open seat in Michigan.

This was the second consecutive election cycle held in a president's sixth year where control of the Senate changed hands, the first being in 2006. This was also the first time that the Democrats lost control of the Senate in a sixth-year midterm election cycle since 1918. With a total net gain of nine seats, the Republicans made the largest Senate gain by any party since 1980. This is also the first election cycle since 1980 in which more than two incumbent Democratic senators were defeated by their Republican challengers. Days after the election cycle, the United States Election Project estimated that 36.4% of eligible voters voted, 4% lower than the 2010 elections, and possibly the lowest turnout rate since the 1942 election cycle.

As of 2022, this remains the last time that a Republican has won a U.S. Senate election in Colorado. This is the most recent Senate election where any Republican flipped an open Democratic-held seat. It also remains the last time that the president's party has suffered a net loss of Senate seats in a midterm election cycle.