Istres is a commune in the département of Bouches-du-Rhône in the Provence-Alpes-Côte d'Azur région of France.
It is the largest commune of metropolitan Ouest-Provence, and is located on the northwest side of the Étang de Berre lagoon, northwest of the city of Marseille. In the 1999 census, Istres had a population of 38,993 inhabitants, the sixth largest in the Bouches-du-Rhône department. The commune has a land area of 113.73 km² (43.911 sq mi). It is the site of the Istres Air Base, and FC Istres (a football team in Ligue 2, the second-highest league in French football).