Fußballclub Gelsenkirchen-Schalke 04 e. V., commonly known as Schalke 04 (German: [ˌʃalkə nʊl ˈfiːɐ̯] ), and abbreviated as S04 (German: [ˈɛs nʊl fiːɐ̯] ), is a professional sports club from the Schalke district of Gelsenkirchen, North Rhine-Westphalia. It is best known for its football team, which plays in the 2. Bundesliga, the second tier of the German football league system, following relegation from the Bundesliga in 2022–23. Other activities offered by the club include athletics, basketball, handball, table tennis, winter sports and eSports.

The \"04\" in the club's name derives from its formation in 1904. Schalke have been one of the most popular professional football teams in Germany, even though the club's heyday was in the 1930s and 1940s. As of 2023, the club has 178,000 members, making it the second-largest football club in Germany and the fourth-largest club in the world in terms of membership.

Schalke have won seven German championships, five DFB-Pokals, one DFB Ligapokal, one DFL-Supercup, one UEFA Cup and two UEFA Intertoto Cups. In 1937, Schalke became the first German club to win the double. Since 2001, Schalke's stadium has been the Veltins-Arena. Schalke hold a long-standing rivalry with Ruhr neighbors Borussia Dortmund, known as the Revierderby.