2018 United States Senate elections

The 2018 United States Senate elections were held on November 6, 2018. Among the 100 seats, the 33 of Class 1 were contested in regular elections while two others were contested in special elections due to Senate vacancies in Minnesota and Mississippi. The regular election winners were elected to six-year terms running from January 3, 2019, to January 3, 2025. Senate Democrats had 26 seats up for election (including the seats of two Independents who caucus with them), while Senate Republicans had nine seats up for election.

To maintain their working majority of 50 senators and their party's vice president's tie-breaking vote, Republicans could only afford a net loss of one seat in these elections. The Republicans had a 52–48 majority after the 2016 elections, but they lost a seat in Alabama after Jeff Sessions resigned to become U.S. attorney general and Doug Jones, a Democrat, won in the subsequent special election. Three Republican-held seats were open as a result of retirements in Tennessee, Utah, and Arizona. Although every Democratic incumbent ran for re-election, Democrats faced an extremely unfavorable map, defending 26 seats, of which 10 were in states won by Donald Trump in the 2016 presidential election, in five states by more than 10%. Republicans, meanwhile, only had to defend nine seats, of which only one was in a state won by Hillary Clinton in 2016.

The Republicans increased their majority by defeating Democratic incumbents in Florida, Indiana, Missouri, and North Dakota, and holding the open seats in Tennessee and Utah. Democrats captured two Republican-held seats, defeating an incumbent in Nevada and winning the open seat in Arizona. This marked the first time that Republicans gained Class 1 Senate seats since 1994. To date, this remains the last time that Democrats won a Senate election in Montana, Ohio, and West Virginia.