Duchy of Lithuania (; ) was a state-territorial formation of ethnic Lithuanians, that existed from the 13th century until 1413. Most of the time it was a constituent part and a nucleus of the Grand Duchy of Lithuania. Other alternative names of the territorial formation, used in different periods, were Aukštaitija or Land of Lithuania (13th century), Duchy of Vilnius (14th – early 15th centuries), Lithuania Propria or simply Lithuania (in a narrow sense).