Pomerania during the High Middle Ages covers the History of Pomerania in the 12th and 13th centuries.
The early 12th century Obodrite, Polish, Saxon, and Danish conquests resulted in vassalage and Christianization of the formerly pagan and independent Pomeranian tribes. Local dynasties ruled the Principality of Rügen (House of Wizlaw), the Duchy of Pomerania (House of Pomerania, "Griffins"), the Lands of Schlawe and Stolp (Ratiboride branch of the Griffins), and the duchies in Pomerelia (Samborides).
The dukes of Pomerania expanded their realm into Circipania and Uckermark to the southwest, and competed with the Kingdom of Poland and the Margraviate of Brandenburg for territory and formal overlordship over their duchies. Pomerania-Demmin lost most of its territory and was integrated into Pomerania-Stettin in the mid-13th century. When the Ratiborides died out in 1223, competition arose for the Lands of Schlawe and Stolp, which changed hands numerous times.
Starting in the High Middle Ages, a large influx of German settlers and the introduction of German law, custom, and Low German language began the process of Germanisation (Ostsiedlung). Many of the people groups that had dominated the area during the Early Middle Ages, such as the Slavic Rani, Lutician and Pomeranian tribes, were assimilated into the new German Pomeranian culture. The Germanisation was not complete, as the Kashubians, descendants of Slavic Pomeranians, dominated many rural areas in Pomerelia. The arrival of German colonists and Germanization mostly affected both the central and local administration.