Thetis Island is a community of approximately 350 year-round residents that expands to almost 2000 during the summer season. It is the smallest of the Southern Gulf Islands, located off the east coast of Vancouver Island and reached by a short ferry ride from Chemainus on Vancouver Island. It is only 4 miles square. It is entirely privately owned with the exception of public roads and 23 miles of public shoreline. It is noted for its easily hiked western shoreline.

The majority of the island is forested and has a Douglas fir ecosystem. There are several wetland areas and a salt marsh. There are some patches of Garry Oak ecosystem on the island, particularly along the southwest facing sandstone bluffs. There are two marinas, one with a pub and restaurant and the other with a café.

Thetis Island's main commercial center is Miners Bay, a village overlooking Active Pass. There are a number of accommodations such as inns, bed and breakfasts, and cottages. There are shops, galleries and artists' studios throughout the island. Community events are held at the agricultural hall and the Thetis Island Fall Fair is the major annual event.

The island received its name from H.M.S. Thetis which was named after Thetis the sea nymph daughter of Zeus. The H.M.S. Thetis surveyed the area from 1851 to 1853.

European settlement came to Thetis in 1873. In 1896 Lawrence Trail was built through the centre of the island to provide access from Preedy Harbour to the Lawrence homestead. Thetis Island and Kuper Island, home of the Penelakut First Nation, were once joined by mud flats was a channel was dredged in 1905 to allow boat traffic.

Visitors to the island enjoy the beautiful shoreline and clear waters where scuba diving, fishing, swimming, sailing, cruising, kayaking, bird watching and hiking are all popular activities.

Thetis Island Accommodations include lodges and properties rented by owners.