Millwall F.C.–West Ham United F.C. rivalry

The rivalry between Millwall and West Ham United is one of the longest-standing and most bitter in English football. The two teams, then known as Millwall Athletic and Thames Ironworks, both originated in the East End of London, and were located under three miles apart. Their supporters were predominantly dockers at shipyards on either side of the River Thames. Consequently, each set of fans worked for rival firms who were competing for the same business; this intensified the tension between the teams. They first played against each other in the 1899–1900 FA Cup. In 1910 Millwall moved south of the River Thames and the teams were no longer East London neighbours. Even so, the derbies retained their passion and both sets of supporters still consider the other club their main rival. Before the First World War the teams met 60 times in just 16 years, mostly in the Southern and Western Football Leagues. The teams have usually competed in different divisions since, spending only 12 seasons in the same tier of the Football League. They have played a total of 39 times in league and cup competitions since 1916.

The rivalry between the teams has been depicted in films that focused specifically on the animosity between the clubs' two hooligan firms, the Inter City Firm and the Millwall Bushwackers. Violence has occurred sporadically between the fans, once resulting in the death of a Millwall supporter in 1976. Most recently in the 2009 Upton Park riot, widespread disorder between supporters in and around West Ham's Upton Park ground led to numerous injuries and a Millwall fan being stabbed before the match began. In the last two games between the sides in the 2011–12 season, the Metropolitan Police implemented London-wide operations to ensure the games were trouble-free. As of the 2016–17 season, West Ham play in the Premier League and Millwall play in the Football League One, two tiers below.