Fußballclub Gelsenkirchen-Schalke 04 e. V., commonly known as FC Schalke 04 ([ɛf tseː ˈʃalkə nʊl fiːɐ̯] (listen)), Schalke 04 ([ˌʃalkə nʊl ˈfiːɐ̯] (listen)), or abbreviated as S04 ([ˈɛs nʊl fiːɐ̯] (listen)), is a professional German football and multi-sports club originally from the Schalke district of Gelsenkirchen, North Rhine-Westphalia. 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. Schalke have played in the Bundesliga, the top tier of the German football league system, since 2022, following promotion from the 2. Bundesliga in 2021–22. As of 2022, the club has 160,000 members, making it the second-largest football club in Germany and the fourth-largest club in the world in terms of membership. Other activities offered by the club include athletics, basketball, handball, table tennis, winter sports and eSports.

Schalke have won seven German championships, five DFB-Pokals, one DFB Ligapokal, one DFL-Supercup and one UEFA Cup. 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 neighbours Borussia Dortmund, known as the Revierderby.

The club was founded on 4 May 1904 as Westfalia Schalke by a group of high school students and first wore the colours red and yellow. The team was unable to gain admittance to the Westdeutscher Spielverband (Western German Football Association) and played in one of the "wild associations" of early German football. In 1912, after years of failed attempts to join the official league, they merged with the gymnastic club Schalker Turnverein 1877 in order to facilitate their entry. This arrangement held up until 1915, when SV Westfalia Schalke was re-established as an independent club. The separation proved short-lived and the two came together again in 1919 as Turn- und Sportverein Schalke 1877. The new club won its first honours in 1923 as champions of the Schalke Kreisliga. It was around this time that Schalke picked up the nickname Die Knappen, from an old German word for "miners" because the team drew so many of its players and supporters from the coal miners of Gelsenkirchen.