By the 10th cent. a.d., when its recorded history began, Pomerania was inhabited by Slavic tribes. It was conquered by Boleslaus I (992-1025) of Poland but became an independent duchy early in the 11th cent. Poland regained control in the 12th cent. and introduced Christianity. The country was split into two principalities. Pomerelia, as E Pomerania came to be known, became independent in 1227, was annexed to Poland in 1294, and was taken in 1308-9 by the Teutonic Knights, who incorporated it into their domain in East Prussia. The histories of Pomerania and Pomerelia after 1308 must be traced separately.

Pomerelia, including Danzig, was formally restored by the Teutonic Knights to Poland at the Treaty of Torun of 1466. Although frequently overrun in the wars of the following three centuries, it remained an integral part of Poland until the first Polish partition (1772), when it passed to Prussia and was constituted into the province of West Prussia. In 1919 part of West Prussia was given to Poland (see Polish Corridor). After the outbreak (1939) of World War II, Germany reannexed the independent state of Danzig and the Pomeranian region of Poland. These areas were returned to Poland in 1945.

Pomerania continued as a duchy of the Holy Roman Empire until the death (1637) of Bogislav XIV, when the region was granted to the elector of Brandenburg. The Peace of Westphalia (1648) gave Hither Pomerania (Vorpommern)—i.e., the western part, with Stettin, Stralsund, and the island of Rügen—to Sweden, while Farther Pomerania (Hinterpommern)—i.e., the eastern part, with Stargard—went to the electorate of Brandenburg (after 1701, the kingdom of Prussia). In 1720, as a result of the Northern War, Sweden lost about half of its part of Pomerania (including Stettin but not Stralsund) to Prussia. In the rest of Swedish Pomerania, the kings of Sweden remained princes of the Holy Roman Empire until the dissolution of the empire in 1806.

Napoleon I overran Swedish Pomerania in the War of the Third Coalition but restored it on making peace with Sweden in 1809. In the Treaty of Kiel (1814), Sweden exchanged Pomerania with Denmark in return for Norway, but at the Congress of Vienna (1815) Denmark ceded its share of Pomerania to Prussia, receiving the duchy of Lauenburg in return. Thus, from 1815 to 1919, all Pomerania and all Pomerelia were in Prussian hands.

Pomerania had by then been thoroughly Germanized; Pomerelia, like the rest of Prussian Poland, was subjected to intense Germanization. After the transfer in 1945 of the larger part of Pomerania to Polish administration, the German-speaking population was largely expelled. The most important cities in the region—Danzig, Stralsund, Stettin, Stargard, Toruń, Chetmno, and Marienburg (Malbork)—were, for a long time, flourishing members of the Hanseatic League; by the 17th cent., however, they had lost the virtual independence they had enjoyed during the greatness of the League.