One of the grands gouvernements in Ancien Régime France, and the smallest of those existing in 1789, Aunis lay on the Bay of Biscay between Saintonge and the coastal regions of Poitou. The Poitevan marshes on the lower course of the Sèvre in the north and other marshes north of the lower Charente in the south helped to isolate it. Its capital was the port of La Rochelle.
Part of the great Duchy of Aquitaine, it was taken from the King of England in 1224 and became part of Poitou. Surrendered to English Aquitaine in 1360 and recovered by France in 1371-2, it became a separate though small province. In the later 16th century it was part of the very large gouvernement of Orléanais and of the généralité of Poitiers. It had become strongly Protestant, and in the 1620s La Rochelle was the last great centre of Protestant military resistance to royal power.
Aunis became a separate gouvernement in the early 17th century, and remained so for the rest of the Ancien Régime: La Rochelle gave it strategic importance. In 1694 Aunis and Saintonge, both pays d’élections, joined together to form the généralité of La Rochelle. Aunis was subject to the Parlement of Paris.
In 1790 most of it became the north of the Department of Charente-Inférieure (now Charente-Maritime), while the rest became part of Deux-Sèvres.