Athletic Club Ajaccio (Corsican: Athletic Club Aiacciu), commonly referred to as AC Ajaccio, ACA or simply Ajaccio, is a French association football club based in the city of Ajaccio on the island of Corsica. The club was founded in 1910 and plays in Ligue 1. The club president is Christian Leca, and the first-team is coached by manager Olivier Pantaloni, following the sacking of Christian Bracconi in October 2014. Ajaccio play their home matches at the Stade François Coty and are rivals with fellow Corsican club Bastia, with whom they contest the Corsica derby (Derby Corse).

Depending on sources, it is agreed that Ajaccio began playing in 1909–10. Their adopted colors are red and white stripes. Though they used to play in what was previously utilised as a sand dump, they decided to move to another, cleaner, safer stadium upon the insistence of Jean Lluis, father-in-law of club president Louis Baretti. The new stadium that was chosen held 5,000 spectators and was in use until 1969.

AC Ajaccio were elected Corsican champions on eight occasions, in 1920, 1921, 1934, 1939, 1948, 1950, 1955 and 1964, and are one of three big "island" teams, along with Gazélec Ajaccio and Bastia, the competition between the three being kept no secret. Spectators during the 1946 Corsican Cup final, held between A.C.A. and Sporting Bastia were handed umbrellas to shield themselves from the violence. Upon refusal of a penalty which would have been awarded to ACA, violence erupted between the fans, who used umbrellas both to cause and shield themselves from violence. This final was abandoned and replayed much later.

A.C.A. became a professional team in 1965 thanks to the ambitious efforts of the club's leaders. They initially adopted the symbol of the polar bear, but this has since been dropped in favour of a more stylised logo that uses a part of the Corsican flag.