The Duchy of Normandy grows out the 911 treaty of Saint-Clair-sur-Epte between King Charles III of West Francia and Rollo, leader of the Vikings, known as Northmen, or Nortmanni in Latin.

The duchy is established under Richard II in c. 996, and from 1106 to 1204 it is held by the Anglo-Norman Plantagenet kings of England.

Normandy is conquered by Philip II of France in 1204 and remains disputed territory until the Treaty of Paris of 1259, when the English sovereigns cede their claim, except for the Channel Islands.The title of "Duke of Normandy" is sporadically conferred in the kingdom of France – the last French "duke of Normandy" having been Louis XVII of France during 1785–1789.