Aunis 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).
The province was officially recognised during the reign of Charles V of France in 1374: "In 1374, Charles V separated La Rochelle from Saintonge to set up a provincial government, comprising the jurisdictions of Rochefort, Marennes and, for a time, Benon. It was thus that Aunis legally became a separate province."
People from Aunis were called Aunisien (masculine) or Aunisienne (feminine). The English term is Aunisian.