Olympique de Marseille ([ɔlɛ̃pik də maʁsɛj], [ɔlɛ̃ˈpikə də maχˈsɛjə]; Occitan: Olimpic de Marselha, [ulimˈpi de maʀˈsejɔ]), also known simply as Marseille or by the abbreviation OM ([o.ɛm], [oˈɛmə]), is a French professional men's football club based in Marseille, Provence-Alpes-Côte d'Azur. Founded in 1899, the club plays in Ligue 1 and have spent most of their history in the top tier of French football. The club has won ten Ligue 1 titles, ten Coupes de France and three Coupes de la Ligue. In 1993, coach Raymond Goethals led the team to become the first and only French club to win the UEFA Champions League, defeating Milan 1–0 in the final, the first under the UEFA Champions League branding of the tournament. In 2010, Marseille won its first Ligue 1 title in 18 years under the management of former club captain Didier Deschamps.

Marseille's home ground is the 67,394-capacity Stade Vélodrome in the southern part of the city, where they have played since 1937. The club has a large fan-base, having regularly averaged the highest attendance in French football. Marseille's average home gate for the 2018–19 season was 50,361, the highest in Ligue 1. The stadium underwent renovation from 2011 to 2014, increasing its capacity to 67,000 ahead of France's hosting of UEFA Euro 2016. In 2015, the club was ranked 23rd globally in terms of annual revenue, generating €130.5 million.

Marseille traditionally play in an all-white kit with sky blue detailing.

In 1997, Marseille was purchased by Franco-Swiss businessman Robert Louis-Dreyfus. Following his death in 2009, his widow Margarita became the club's majority shareholder in 2010. In 2016, American businessman Frank McCourt bought the club from her, and appointed businessman Jacques-Henri Eyraud as the club president, although he was replaced by Pablo Longoria in 2021.