(also Saare-Läänemaa or Ösel-Vikskim Episcopate), a feudal state that was located in northwestern Estonia and included the province of Läänemaa and parts of the islands of Saaremaa and Hiiumaa. The total area of the Ösel Episcopate was approximately 7,600 sq km.
The episcopate arose as a result of the conquest of Estonia in late 1227 or early 1228 by the Order of Knights of the Sword, which subsequently, in 1237, merged with the Teutonic Order to form the Livonian Order. The state, which assumed its definitive form in 1234, was headed by a bishop who was a vassal of both the Holy Roman emperor and the pope. The bishop’s see was first located at Lihula, but it was moved to Pärnu in 1251 and then to Haapsalu circa 1265.
During the 13th and 14th centuries, the Livonian Order strove to establish a unified Livonian state that would include the Ösel Episcopate. After the order was defeated by Russia in the Livo nian War of 1558–83, the bishop sold his holdings in 1559 to the Danish king, Frederick II, who granted them to his brother Duke Magnus in 1560. Although the Ösel Episcopate was subordinated to Denmark in 1561, it survived as a separate entity on the is land of Saaremaa until 1573.