The Duchy of Pomerania (German: Herzogtum Pommern, Polish: Księstwo Pomorskie, 12th century – 1637) was a duchy in Pomerania on the southern coast of the Baltic Sea, ruled by dukes of the House of Pomerania (Griffins).
The duchy originated from the realm of Wartislaw I, a Slavic Pomeranian duke, and was extended by the Lands of Schlawe and Stolp in 1317, the Principality of Rügen in 1325, and the Lauenburg and Bütow Land in 1455. During the High Middle Ages, it also comprised the northern Neumark and Uckermark areas as well as Circipania and Mecklenburg-Strelitz.
The Duchy of Pomerania was established as a vassal state of Poland in 1121, which it remained until the fragmentation of Poland after the death of Polish ruler Bolesław III Wrymouth in 1138. Afterwards the Dukes of Pomerania were independent, and later were vassals of the Duchy of Saxony from 1164 to 1181, of the Holy Roman Empire from 1181 to 1185, of Denmark from 1185 to 1227 and the Holy Roman Empire again from 1227 to 1806 (including periods of vassalage to the Margraves of Brandenburg). Most of the time, the duchy was ruled by several Griffin dukes in common, resulting in various internal partitions. After the last Griffin duke had died during the Thirty Years' War in 1637, the duchy was partitioned between Brandenburg-Prussia and Sweden. The Kings of Sweden and the Margraves of Brandenburg, later Kings of Prussia, became members as Dukes of Pomerania in the List of Reichstag participants.