Thailand (ˈtaɪlænd ty-land or ˈtaɪlənd; Thai: ราชอาณาจักรไทย Ratcha Anachak Thai, or ประเทศไทย Prathet Thai IPA: [râːtɕʰa ʔaːnaːtɕɑ̀k tʰɑj]), officially the Kingdom of Thailand and formerly known as Siam (Thai: สยาม; RTGS: Sayam), is a country located at the center of 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 kingdom, with most recorded reigns in the world; a constitutional monarchy with King Rama IX, the ninth king of the House of Chakri, who has reigned since 1946, making him the world's longest-serving current head of state and the longest-reigning monarch in Thai history. The king is officially titled Head of State, the Head of the Armed Forces, an Upholder of the Buddhist religion, and the Defender of all Faiths.