Ko Samui (or Koh Samui, Thai: เกาะสมุย) is an island off the east coast of the Kra Isthmus in Thailand, close to the mainland Surat Thani town. It is Thailand's second largest island, with an area of 228.7 km² and a population of 47,874 (2006).
The island was probably first inhabited about 15 centuries ago, settled by fishermen from Malay Peninsula and Southern China. It appears on Ming Dynasty maps dating back to 1687, under the name Pulo Cornam. The name Samui is mysterious in itself. Perhaps it is an extension of the name of one of the native trees, mui, or it is a corruption of the Chinese word Saboey, meaning "safe haven".