Ko Tao (also often Koh Tao, Thai: เกาะเต่า, Thai pronunciation: [kɔ̀ʔ tàw], lit. "Turtle Island") is an island in Thailand and forms part of the Chumphon Archipelago on the western shore of the Gulf of Thailand. It covers an area of about 21 km². Administratively it forms a district (amphoe) (as of 2013) of Surat Thani Province. As of 2006 its official population was 1,382. The main settlement is Ban Mae Hat.
The economy of the island is almost exclusively centred on tourism, especially scuba diving.
Ko Tao was named by its first settlers after the island's turtle-like shape. Coincidentally, the island is an important breeding ground for hawksbill and green turtles. Development of tourism has negatively impacted the health of these grounds but a breeding programme organised in 2004 by the Royal Thai Navy and KT-DOC, a coalition of local scuba diving centres, has reintroduced hundreds of juvenile turtles to the island's ecosystem.
Initially the island was uninhabited, with only the occasional fisherman from the neighbouring islands, looking for shelter in a storm or just resting before continuing on his journey.