Archaeological discoveries around the northeast village hamlet of Ban Chiang suggest that the world's Bronze Age civilization was flourishing in Thailand some 5,600 years ago. Successive waves of immigrants, including Mon, Khmer and Thai, gradually entered the land mass now known as Thailand, mostly slowly travelling along fertile river valleys from southern China. By the early 1200s, the Thai people had established small northern city-states in Lanna, Phayao, and Sukhothai. In 1238, two Thai Chieftains rebelled against Khmer suzerainty and established the first truly independent Thai kingdom in Sukhothai (literally, "Dawn of Happiness").

At approximately the same time, King Mengrai, an ally of Sukhothai was establishing the northern Lannathai Kingdom, centered on Chiang Mai, which was founded in 1296.

The Sukhothai era saw the Thais' gradual expansion throughout the entire Chao Phraya River basin, the establishment of Theravada Buddhism as the predominant Thai religion, the creation of the Thai Alphabet and the first expression of developing Thai art forms, including painting, sculpture, architecture and literature.

The Sukhothai era declined in the 1300s and eventually became a vassal state of Ayutthaya, a dynamic young kingdom further south in the Chao Phraya River valley. Founded in 1350, Ayutthaya remained the Thai capital until 1767 when Burmese invaders destroyed it.

During Autthaya' s 417 years as the capital, under the rules of 33 kings, the Thai brought their distinctive culture to full fruition, totally riding their lands of Khmer presence and fostering contact with Arabian, Indian, Chinese, Japanese and European power. Ayutthaya' s destruction was as serve a blow to a Thais, as loss of the Paris or London would have been to the French or English. However, a Thai revival occurred within a few months, and King Taksin who later made Thonburi his capital expelled the Burmese. In 1782, the first king of the present Chakri dynasty, Rama I, established his new capital on the site of the riverside village called Bangkok (Village of Wild Plums).

Two Chakri monarchs, Mongkut (Rama IV), who reigned between 1851 and 1868, and his son Chulalongkorn (Rama VB), who reigned from 1868 to 1920, saved Thailand from western colonization through adroit diplomacy and selective modernization.

Today, Thailand has a constitutional monarchy. Since 1932, Thai kings including the present monarch, H.M. King Bhumipol Adulyadej, have exercised their legislative powers through a national assembly, their executive powers through a cabinet headed by a Prime Minister and their judicial power to the law courts.