Moster is a former municipality in the old Hordaland county, Norway. The municipality existed from 1916 until 1963, when it was merged into the new, larger municipality of Bømlo. The administrative centre of the municipality was the village of Mosterhamn, where the Old Moster Church is located. The 66-square-kilometre (25 sq mi) municipality encompassed the southeastern part of the island of Bømlo and the island of Moster as well as many surrounding islets.