The flag of the Kingdom of Thailand shows five horizontal stripes in the colours red, white, blue, white and red, with the middle blue stripe being twice as wide as each of the other four. The design was adopted on 28 September 1917, according to the royal decree about the flag in that year; the Thai name for the flag is ธงไตรรงค์ (Thong Trairong), meaning tricolour flag. The colours are said to stand for nation-religion-king, an unofficial motto of Thailand, red for the land and people, white for Theravada Buddhism and blue for the monarchy, as having been the auspicious colour of King Rama VI. As the king had declared war on Germany that July, some note the flag now bore the same colours as those of Britain and France.

The Flag Act of BE 2522 (1979 CE) stipulates the design of national flag as "a rectangle 6 portions in width and 9 portions in length, vertically divided into five full-length horizontal stripes: at the middle, a dark blue stripe 2 portions wide; flanking the blue stripe, two white stripes 1-portion-wide each; and outwardly flanking the white stripes, two red stripes 1-portion-wide each. The flag shall also to be known as the Trairanga."

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.