Ain (; French: [ɛ̃] ; Arpitan: En) is a French department in the Auvergne-Rhône-Alpes region, Eastern France. Named after the Ain river, it is bordered by the Saône and Rhône rivers. Ain is on the country's eastern edge, on the Swiss border, where it borders the cantons of Geneva and Vaud. In 2019 it had a population of 652,432.

Ain is composed of four geographically different areas - (Bresse , Dombes, Bugey and Pays de Gex) - each of which contributes to the diverse and dynamic economic development of the department. In Bresse agriculture and agro-industry are dominated by the cultivation of cereals, cattle breeding, milk and cheese production as well as poultry farming.