Val d'Aran, a small valley (620.47 km2) is a comarca (county) in the northwestern part of Catalonia, which is an autonomous region of Spain. Most of the valley constitutes the only Catalan territory on the north face of the Pyrenees, hence the only part of Catalonia whose waters drain into the Atlantic Ocean. The region is characterized by an Atlantic climate, due to its peculiar orientation, which is different from other valleys in the area.

The Val d'Aran borders on the North with France, with Aragón on the west and with the Catalan comarques of Alta Ribagorça to the south and Pallars Sobirà to the east. The capital of the comarca is Vielha, with 3,692 inhabitants (1996). The entire population of the valley is about 7,130 (1996). The chief river is the Garona, which descends through Gascony to the Atlantic. The Noguera Pallaresa, with its head only a hundred meters from that of the Garona, flows the other way, toward the Mediterranean.

The valley used to be without direct communication with the south side of the mountains during winter, until the construction of a tunnel, opened in 1948. Spanish Republican guerrillas (supporters of the Second Spanish Republic, the losing side in the Spanish Civil War) controlled the area from the end of World War II until the opening of the tunnel.