Bayer 04 Leverkusen is a German football club based in Leverkusen, North Rhine-Westphalia.The club plays in the Bundesliga, the top tier of the German football league system, and hosts matches at the BayArena. The club was founded in 1904 by employees of the German pharmaceutical company Bayer, whose headquarters are in Leverkusen and from which the club draws its name.