The Duchy of Gascony (also Vasconia; French: duché de Gascogne, duché de Vasconie; Basque: Baskoniako dukerria) is a duchy in present southwestern France, roughly corresponding to the modern region of Gascony after 824.

The Duchy of Gascony, originally known as Wasconia, is initially a Frankish march formed to hold sway over the Basques (Vascones).

However, the Duchy goes through different periods, from its early years with its distinctively Basque element to the merge in personal union with the Duchy of Aquitaine to the later period as a dependency of the Plantagenet kings of England.In the Hundred Years' War, Charles V of France conquers most of Gascony by 1380, and under Charles VII of France it is incorporated into the kingdom of France in its entirety in 1453.