Lille Olympique Sporting Club (French pronunciation: [lil ɔlɛ̃pik spɔʁtɪŋ klœb]), commonly referred to as LOSC, LOSC Lille or simply Lille, is a French professional football club based in Lille, Northern France competing in Ligue 1, the top division of French football. Lille have played their home matches since 2012 at the Stade Pierre-Mauroy. The 50,186-capacity retractable roof venue is the fourth-largest stadium in France.

Lille were 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 were the league's inaugural champions. The club's most successful period was the decade from 1946 to 1956, in the post-war period, when the first-team 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, their fourth league title in 2021 as well as their first Trophée des Champions the same year, Lille are the fourth best French club in the 21st century.

In domestic football, the club has won a total of four league titles, six Coupes de France and one Trophée des Champions since its foundation. In European football, Lille have participated in the UEFA Champions League nine times, reaching the knockout phase three times, competed in the UEFA Europa League on nine occasions and got to the UEFA Conference League quarter-finals once. They also won the UEFA Intertoto Cup in 2004 after finishing as runners-up in 2002. Lille are also one of the few clubs, still in the first division, to have at least 15 final top-three appearances in the history of the French championship.

Nicknamed Les Dogues (French for \"The Mastiffs\"), Lille are known for their academy which has produced and trained notable graduates. Throughout their history, they have cultivated a reputation for scouting and developing young players. Lille is the best club in the world regarding the financial balance of transfers concerning non-academy players signed since 2015, according to the CIES Football Observatory. They have a long-standing rivalry with nearby side Lens, in which Lille lead in the head-to-head record and in terms of total trophies won. Chaired by Olivier Létang, they are the fifth-most followed French sports club on social media.