United States Senate elections, 2018 (A New American Century)

The 2018 United States Senate elections were held on November 6, 2018. Thirty-three of the 100 seats were contested in regular elections while two others were contested in special elections due to Senate vacancies in Minnesota and Mississippi. The 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 Republican Vice President Nikki Haley (who can cast a tie-breaking vote), Republicans could only afford a net loss of one Senate seat in the 2018 elections. The Republicans had a 53-47 majority after the 2016 Senate elections. Two Republican-held seats were open as a result of retirements in Tennessee and Utah, while every Democratic incumbent ran for reelection. Democrats faced what was considered an extremely unfavorable map as they were defending twelve seats in states won by Marco Rubio in the 2016 presidential election and 26 in total while Republicans weren't defending any seats in a state won by Hillary Clinton in 2016 and nine in total. Additionally, Democrats were defending five seats in states that Rubio won by double digits in 2016.

The Republicans maintained a Senate majority following the 2018 elections defeating Democratic incumbents in Florida, Indiana, Missouri, North Dakota, Montana, Michigan, and New Jersey. Democrats won two Republican-held seats, defeating incumbent Dean Heller in Nevada and winning an open seat in Mississippi after Democrat Mike Espy defeated embattled, controversial Republican candidate Cindy Hyde-Smith.