About sixty million of Thai population embraces four major ethnic groups. Almost 80% are Thais; others are ethnic Chinese 8-12%, Malay 4-6%, and minority group 3-5%. The origin of Thai people has been a problematic subject among the academics as there are several theories given about Thai origin. Most widely accepted theory is that Tai people migrated south from the southern China due to the Mongol invasion in the 12th century in to the mainland Southeast Asia. However, recent studies based on archeological finds in Ban Chiang, Thailand argue that at least about 4,000 years ago, there already had been Thais living in this region and that they had developed their own culture. Until today, conclusion about the Thai origin is still unreachable.

It is quite difficult to find the typical physiognomy or physique as various ethnic groups like the Mons, Burmese, or Khmers have assimilated to a degree that they are all similar in appearance. What distinguishes Thai people into group is a dialect. Different dialect is in accordance with the regional division as well. There are four regional divisions with their different dialects: Central Thais, Northern Thais, Northeastern Thais, and Southern Thais.

Central Thais are the majority of total population, speaking Central Thai language. This is the political, social, and culturally dominant group, concentrating in the Chao Praya River Basin. Political power, economy, culture, education, and development are all centered in the central region. Central Thai dialect is designated to be an official language and taught in all public schools.

Northeastern Thais are the second-large ethnic group in Thailand. They are called Thai-Lao who have close relation to Lao people in the former Lan Xang Kingdom (Land of Million Elephants), encompassing the area of Laos and most of Korat Plateau (Northeastern region). They migrated across the Mekong River and still retain their language and tradition under the rule of semi-autonomous Lao princes until the early 20th century before completely incorporated with Thai government. The region considered to be relatively laid-back for its remoteness from the central government. However, development programs have been launched to improve living-condition of poor residents in the region. Nowadays, most northeastern Thais accept the benefits of Thai citizenship while remaining their distinct language and tradition of Laotian ethnicity.

Northern Thais are another ethnic group whose culture and language are distinct from the central ones. They called themselves "Khon Muang", People of the region. It is the northern Thais who founded the first major Thai kingdom, Lanna Kingdom in the early 13th century before the rise of Sukhothai. Northern Thais are proud of their language which is closely related to one of the Shan in Burma. There are also other northern dialects spoken by other ethnic groups such as the Mons near Lamphun as well as the tribal languages of the Karen, Hmong, Akha, Lahu, and Lisu. As other regions, central Thai dialect is taught in all public schools, radio, and television even if most of northern Thais still speak their own dialect in daily life.

Southern Thais are characterized by their physiognomy distinctly different from that of northern peoples- darker, with larger eyes and rounder faces which represent the Thai-Malay mixed characteristics. Southern culture was built up from different Asian civilizations. Among the major ones were the Indians, Buddhist Mons, Malay-Indonesians and Srivijayans, and Khmers. All have influence typical southern culture represented as food, architecture, performing arts and ceremonies. Southern Thais speak more abbreviated language with shorten word and quick rhythm. Even the residents of Bangkok have difficulty understanding their patter.