The Tapi (or Tapee) river (Thai: แม่น้ำตาปี, RTGS: Maenam Tapi, Thai pronunciation: [mɛ̂ːnáːm tāːpīː]) is the longest river in southern Thailand. The river originates at the Khao Luang, and has a wide estuary into the Gulf of Thailand at Bandon Bay near the town of Surat Thani. It has a length of 230 km.

The river drains an area of 5460 km² and in 1997 had an annual discharge of 135.4 m³/s or 4.3 km³ per year. The Phum Duang River (or Khiri Rat River), which drains another 6,125 km² west of the Tapi watershed, joins the estuary 15 km west of Surat Thani in Amphoe Phunphin.

The river was named in August 1915 after the river Tapi in India, shortly after the town of Surat Thani was named after the town Surat.

The island of Ko Lamphu (เกาะลำพู) is located in the Tapi River, about 9 km from its mouth, right by the Surat Thani town center.

In 1975 an area of 29.6 km² of swamp land on the east bank of the river in the district Khian Sa was declared the Nong Thung Thong non-hunting area.

Coordinates: 9°11′50″N 99°22′57″E / 9.19722°N 99.3825°E / 9.19722; 99.3825

Thailand ( /ˈtaɪlænd/ TY-land or /ˈtaɪlənd/;Thai: ประเทศไทย, RTGS: Prathet Thai), officially the Kingdom of Thailand (Thai: ราชอาณาจักรไทย, RTGS: Ratcha Anachak Thai; IPA: [râːt.tɕʰā ʔāːnāːtɕàk tʰāj] ( listen)), formerly known as Siam (Thai: สยาม; RTGS: Sayam), is a country located at the centre of the Indochina peninsula in Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the west by the Andaman Sea and the southern extremity of Burma. Its maritime boundaries include Vietnam in the Gulf of Thailand to the southeast, and Indonesia and India in the Andaman Sea to the southwest.

The country is a constitutional monarchy, headed by King Rama IX, the ninth king of the House of Chakri, who, having reigned since 1946, is the world's longest-serving head of state and the longest-reigning monarch in Thai history. The king of Thailand is titled Head of State, Head of the Armed Forces, the Upholder of the Buddhist religion, and the Defender of all Faiths.

There are two rivers named Tapi