Fußballclub Union Berlin e. V., commonly known as 1. FC Union Berlin is a professional German association football club based in Köpenick, Berlin. The club emerged under the current name in 1966 but its origins can be traced back to 1906 when its predecessor FC Olympia Oberschöneweide was founded. From 2009 until 2019, they competed in the 2. Bundesliga, the second tier of German football. In 2019, after defeating VfB Stuttgart in the relegation play-offs, Union won promotion to the Bundesliga top flight for the first time in the club's history, for the 2019–20 season.
Union was based in the East Berlin sector of the city, joining the common German league structure upon the reunification of the city and the country in 1990.
The home ground Stadion An der Alten Försterei (Stadium by the Old Forester's House) is the largest single-purpose football stadium in the German capital having a capacity of 22,012.
It has been home to Union Berlin and its forerunners since it was opened in 1920. The stadium became internationally famous for concerts and events like the annual Weihnachtssingen (Christmas Carols Event) and the WM-Wohnzimmer (World Cup Living Room) in 2014.
The club has become well known for its enthusiastic and creative fan base and for its chant "Eisen Union" (Iron Union).