Istres is a commune in southern France, some 60 km (38 mi) northwest of Marseille. It is in the Provence-Alpes-Côte d'Azur region, in the Bouches-du-Rhône department, of which it is a subprefecture. Its inhabitants are called Istréens.
Istres is adjacent to the étang de Berre lagoon (the largest in Europe) and the étang de l'Olivier lagoon. It is located some 60 km (38 mi) north-west of Marseille, 20 km (13 mi) south-west of Salon-de-Provence, 10 km (6 mi) north of Martigues and 45 km (28 mi) south-east of Arles. Istres is also adjacent to the plaine de la Crau and the Camargue national park.