The Duchy of Gascony or Duchy of Vasconia was a duchy located in present-day southwestern France and northeastern Spain, an area encompassing the modern region of Gascony. The Duchy of Gascony, then known as Wasconia, was originally a Frankish march formed to hold sway over the Basques. However, the duchy went through different periods, from its early years with its distinctively Basque element to the merger in personal union with the Duchy of Aquitaine to the later period as a dependency of the Plantagenet kings of England.

The Duchy of Aquitaine was a historical fiefdom in western, central, and southern areas of present-day France to the south of the river Loire, although its extent, as well as its name, fluctuated greatly over the centuries, at times comprising much of what is now southwestern France (Gascony) and central France.