Bayer 04 Leverkusen, officially known as Bayer 04 Leverkusen Fußball GmbH (German: [ˌbaɪ̯ɐ ˈleːvɐˌkuːzn̩]) and commonly known as Bayer Leverkusen or simply Leverkusen, is a German professional football club based in Leverkusen, North Rhine-Westphalia. It competes in the Bundesliga, the top tier of German football, and plays its home matches at the BayArena.

Founded in 1904 by employees of the pharmaceutical company Bayer (whose headquarters are in Leverkusen and from which the club draws its name), the club was formerly the best-known department of TSV Bayer 04 Leverkusen and RTHC Bayer Leverkusen, sports clubs whose members participate in athletics, gymnastics, basketball, field handball, rowing, tennis and hockey. In 1999, the football department was separated from the sports club.[6] Bayer Leverkusen's main colours are red and black, which feature across their playing kits and on their badge, and their local rivals are 1. FC Köln, Borussia Mönchengladbach and Fortuna Düsseldorf.

Bayer Leverkusen were promoted to the Bundesliga in 1979 and won their first top-flight honour, the UEFA Cup, in 1988, then the DFB Pokal in 1993. The club infamously finished runners-up across three competitions in 2002, including the UEFA Champions League. After more than 30 years without silverware, the club won their first ever Bundesliga title in 2024 as well as the DFB Pokal, becoming the first German team to do so unbeaten, the first German team to complete an unbeaten domestic double, and set the European record for consecutive unbeaten competitive games (51).