Aunis (French: [onis, oni]) is a historical province of France, situated in the north-west of the department of Charente-Maritime. Its historic capital is La Rochelle, which took over from Castrum Allionis (Châtelaillon) the historic capital which gives its name to the province.
It was a fief of the Duchy of Aquitaine. It extended to Marais Poitevin in the north, Basse Saintonge (and Niortais) in the east, and Rochefortais in the south. Aunis had an influence approximately 20–25 km into the Isle of Ré (l'Île de Ré).