The Port Authority of Thailand (PAT) is a state corporation of Thailand, responsible for the regulation and governance of the ports of Thailand, primarily the ports of Laem Chabang and Bangkok, the country's two largest ports. PAT operates Thai ports in conjunction with public companies including Hutchison Ports Thailand and PSA International. The Port Authority is located in Bangkok.

The PAT was founded by the Port Authority of Thailand Act 1951, as an autonomous government agency under the jurisdiction of the Ministry of Transportation and Communications. In 1961 construction was begun on the port of Laem Chabang, due to overcrowding at the river port of Bangkok, and by 1997 Laem Chabang had become the country's busiest seaport. In 2000 the Port Authority of Thailand was converted from a government agency to a state corporation by amendment to the Port Authority of Thailand Act 1951.

Ports under the governance of PAT include those of Bangkok, Laem Chabang, Chieng Saen, Chieng Khong, Ranong, as well as the Bangkok Coastal and Barge Domestic Terminal.

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.

In Canada and the United States a port authority (less commonly a port district) is a governmental or quasi-governmental public authority for a special-purpose district usually formed by a legislative body (or bodies) to operate ports and other transportation infrastructure.

Port authorities are usually governed by boards or commissions, which are commonly appointed by governmental chief executives, often from different jurisdictions. For example, in Canada the federal Minister of Transport selects one board member, the local chief executive one, and the rest of the board are at the recommendation of port users to the federal Minister. In Canada all port authorities have a federal or Crown charter called Letters Patent.

Most port authorities are financially self-supporting. In addition to owning land, setting fees, and sometimes levying taxes, port districts can also operate shipping terminals, airports, railroads, and irrigation facilities.

In Mexico the federal government created sixteen port administrations in 1994–1995 called Administración Portuaria Integral (API) in Spanish, as result of the Ley de Puertos of 1993. These are organized as variable capital corporations (Sociedad Anónima de Capital Variable or S.A. de C.V.), with the intent of creating more private investment in a state owned sector.