Rotherham United Football Club, nicknamed The Millers, is a professional football club based in Rotherham, South Yorkshire, England, which compete in the EFL Championship. The club's colours were initially yellow and black, but changed to red and white around 1930. Since 2012 they have played home matches at the New York Stadium, having briefly moved to the Don Valley Stadium from their original home at Millmoor in 2008.

The club was formed as a merger between Rotherham County and Rotherham Town in 1925 and were immediately placed in the Football League. They won promotion as champions of the Third Division North in 1950–51 and were beaten finalists in the inaugural League Cup final in 1961, losing to Aston Villa 3–2 on aggregate. After seventeen seasons in the Second Division, relegations followed in 1968 and 1973. Promotion from the Fourth Division was secured in 1974–75 and the club went on to win the Third Division title in 1980–81. Relegations in 1983 and 1988 gave Rotherham the opportunity to win the Fourth Division title in 1988–89, though they had to win another promotion in 1991–92 following relegation the previous season. They beat Shrewsbury Town 2–1 in the 1996 final of the Football League Trophy.

Under the stewardship of Ronnie Moore, Rotherham secured back-to-back promotions in 1999–2000 and 2000–01. They stayed in the second tier for four seasons, though were relegated twice in three years by 2007. The club again secured back-to-back promotions, this time under Steve Evans, securing automatic promotion from League Two in 2012–13 and promotion from League One via the play-offs in 2013–14. The club have moved between the Championship and League One for six successive seasons between 2016–17 and 2021–22, winning the play-offs in 2018 as well as the 2022 EFL Trophy final.