Lille Olympique Sporting Club ([lil ɔlɛ̃pik spɔʁtɪŋ klœb]), commonly referred to as LOSC, LOSC Lille or simply Lille, is a French professional football club based in Lille, Hauts-de-France that competes in Ligue 1, the top flight of French football. Lille has played its home matches since 2012 at Stade Pierre-Mauroy, the fourth-largest football stadium in France. The 50,186-capacity retractable roof venue replaced the club's previous home of Stadium Lille-Metropole.

Lille was founded as a result of a merger between Olympique Lillois and SC Fives in 1944. Both clubs were founding members of the French Division 1 and Olympique Lillois was the league's inaugural champions. In domestic football, the club has won four league titles, six Coupes de France and one Trophée des Champions since its foundation. In European football, Lille has participated in the UEFA Champions League eight times, reaching the knockout phase twice, competed in the UEFA Europa League on eight occasions and won the UEFA Intertoto Cup in 2004 after finishing as runners-up in 2002.

The club's most successful period was the decade from 1946 to 1956, in the post-war period, when the team led by managers George Berry and André Cheuva won seven major trophies, including a League/Cup double in 1946, and was known as La Machine de Guerre (French for "The War Machine"). Having won another double in 2011, its fourth league title in 2021 as well as its first French super cup, Lille is the fourth best French club in the 21st century.

Nicknamed Les Dogues (French for "The Mastiffs"), the club has a long-standing rivalry with nearby side Lens, with whom they contest the Derby du Nord. Lille leads in the head-to-head record between the two rivals and in terms of total trophies won. Currently owned by Luxembourg-based investment fund Merlyn Partners SCSp, it's the fifth-most followed French sports club on social media.