The "Diois" (pronouce Dee-wah), is a Drôme valley region which spreads from the town of Saillans, in the west to Rousset pass in the north, Menée, Grimone and Cabre passes in the east. Diois is the upper and central part of the Drôme valley

The river makes a large detour between the towns of Saillans and Luc-en-Diois.

The Diois region is dominated by the Glandasse mountain, which is the southern extension of the Vercors highland.

Several rivers, of which the Roanne river (the bigest tributary of the Drôme river), irrigate a landlocked territory in the east-center of the Drôme department, at the border of Hautes-Alpes department (Gap).

The main access is from the Rhône valley, in the west (Valence, Crest) but other roads also lead to the Diois:

-Menée pass (from Grenoble);

-Cabre pass (from Gap);

-Rousset pass (from Vercors);

-Premmol pass (from Nyons)....

The Diois region was once inhabited by the Vocontii  (Voconces), a Gallic people who lived on the east bank of the Rhône. They were a romanised population, which had as northern capitals Luc-en-Diois (Lucus augusti) and then Die (Dea Augusta Vocontiorum). Vaison la Romaine (Vasio Vocontiorum), in Vauclus department, was the southern capital.

Texts from VI century made reference to the Diois region as Civitas Diensis (Diois city), which was a small province of the ancient France, part of lower Dauphiné region, between Valence and Gap.