West Ham United Football Club is an English professional football club based in Stratford, East London that competes in the Premier League, the top tier of English football. The club plays at the London Stadium, having moved from their former home, the Boleyn Ground, in 2016.

The club was founded in 1895 as Thames Ironworks and reformed in 1900 as West Ham United. They moved to the Boleyn Ground in 1904, which remained their home ground for more than a century. The team initially competed in the Southern League and Western League before joining the Football League in 1919. They were promoted to the top flight in 1923 when they were also losing finalists in the first FA Cup Final held at Wembley. In 1940, the club won the inaugural Football League War Cup.

West Ham has been winners of the FA Cup three times; in 1964, 1975 and 1980, and have also been runners-up twice; in 1923 and 2006. The club has reached two major European finals, winning the European Cup Winners’ Cup in 1965 and finishing runners-up in the same competition in 1976. West Ham also won the Intertoto Cup in 1999. They are one of eight clubs never to have fallen below the second tier of English football, spending 63 of 95 league seasons in the top flight, up to and including the 2020–21 season. The club’s highest league position to date came in 1985–86 when they achieved third place in the then First Division.

Three West Ham players were members of the 1966 World Cup final-winning England team: captain Bobby Moore and goalscorers Geoff Hurst and Martin Peters. The club has a long-standing rivalry with Millwall, and the fixture between the two teams has gained notoriety for frequent incidents of football hooliganism. West Ham adopted their claret and sky blue colour scheme in the early 1900s, with the most common iteration of a claret shirt and sky blue sleeves first emerging in 1904.