Anvil Island, also often called Hat Island, is the third-largest of the islands in Howe Sound, British Columbia, Canada, and the northernmost of the major islands in that sound. It is located northeast of Gambier Island and southwest of Britannia Beach and west of Porteau Cove. The Defence Islands are to its northeast and are Indian Reserves of the Squamish Nation. A summer camp, Daybreak Point Bible Camp, operates on the south of the island, and some summer homes are located there.