Thailand's population can be generally categorized into the Central Thai, the Northeastern Thai or Isan (see special section on this region), the Northern Thai, and the Southern Thai. The Central Thai have long dominated the nation politically, economically, and culturally, even though they make up only about one-third of Thailand's population and are slightly outnumbered by the Northeastern Thai. Due to the education system and the forging of a national identity, many people are now able to speak Central Thai as well as their own local dialects.

The largest group of non-Thai people are the Chinese who have historically played a disproportionately significant role in the economy. Many have assimilated into mainstream Thai society, and do not live in Bangkok's Chinatown on Yaowarat Road. Other dominant ethnic groups include Malays in the south, Mon, Khmer and various hill tribes. After the end of the Vietnam War, many Vietnamese refugees settled in Thailand, mainly in the northeastern region.

The Thai language is Thailand's national language, written in its own alphabet, but many ethnic and regional dialects exist as well as areas where people speak predominantly Isan or Mon-Khmer languages. Although English is widely taught in schools, its use is not widespread throughout the country.