Lithuania Minor (Lithuanian: Mažoji Lietuva; German: Kleinlitauen; Polish: Litwa Mniejsza; Russian: Máлая Литвá) or Prussian Lithuania (Lithuanian: Prūsų Lietuva; German: Preußisch-Litauen, Polish: Litwa Pruska) is a historical ethnographic region of Prussia, later East Prussia in Germany, where Prussian Lithuanians or Lietuvininkai once lived in.
The Lithuanian-speaking Prussians were concentrated in the northeast East Prussia (Lithuania Minor). The Germanic Teutonic Knights invaded the region in the 13th century and over time the Baltic Old Prussian ethnic group became completely Germanized and the Old Prussian language had sadly died out during the 18th century. Lithuanian proper still lingered on until World War II in the Klaipėda Region, but later gained much ground after the region's annexation by the USSR (along side Russian). Lithuanian has gained even more after Lithuania left the USSR.
Now only the small Klaipėda Region portion of the former Lithuania Minor is within the borders of modern Lithuania, while some is in Poland, most of the territory is now part of the Kaliningrad Oblast of Russia.