Moster is an island in Bømlo municipality in Vestland county, Norway. The 12-square-kilometre (4.6 sq mi) island lies just south of the large island of Bømlo, surrounded by the Bømlafjorden. The Røyksund Channel is a small navigable channel that separates Moster from the island of Bømlo. There is one bridge on the Norwegian County Road 542 that crosses the channel, connecting the island to the rest of the municipality, which in turn is connected to the mainland via the Triangle Link.