The official language of Thailand.

The Thai name for the language is ภาษาไทย (phasa thay), which translates literally as "the language of Thai".

Thai is part of the Tai languages group of the Tai-Kadai language family. The Tai-Kadai languages are thought to have originated in southern China, and some linguists have speculated links to the Austroasiatic, Austronesian, or Sino-Tibetan language families.

It is a tonal and analytic language.

Standard Thai, also known as Central Thai or Siamese, is the official language of Thailand, spoken by about 25 million people (1990). Bangkok Thai can be included in Standard Thai or considered as a separate dialect. Khorat Thai is a recognized dialect of Thai, spoken by about 400,000 (1984) in Nakhon Ratchasima.

In addition to Standard Thai, Thailand is home to several other related Tai languages.

The Thai alphabet is probably derived from the Old Khmer (อักขระเขมร) script, which is a southern Brahmic script of the Indic family.

From the perspective of linguistic typology, Thai can be considered to be an analytic language. As in many Asian languages, the Thai pronominal system varies according to the sex and relative status of speaker and audience.

Nouns are uninflected, and there are no plural forms. Plurals are expressed by adding "nouns of multitude" (ลักษณนาม) or classifiers in the form of noun-number-classifier, e.g. "teacher five person" for "five teachers".

Thais use two systems for telling the time: the 24-hour clock and the traditional Thai six-hour clock. The latter system has been used in some form since the days of the Ayutthaya kingdom, but was codified in its present form in 1901 by King Chulalongkorn (in Royal Gazette 17:206) and is widely used in colloquial speech. It works by dividing the day into four equal parts, then counting the hours within each part. However most commonly used nowadays is a combination of the traditional six hour counting with a twelve hour counting, thus the numbering of the hours of the second and fourth quarter starts from 7 instead from 1.