Standard Thai is the official language of Thailand, spoken by about 50 million people in Thailand and Southern China. Various dialects are spoken by many more in Thailand, and can be generally understood by all.

The Thai language, formerly Siamese, is spoken throughout Thailand and has several forms for different social contexts:

• Informal Thai - without polite terms of address, used between relatives and friends
• Elegant Thai - official and written version, includes respectful terms of address. Simplified form used in written media
• Thai for public speaking
• Religious Thai (heavily influenced by Sanskrit) used when discussing Buddhism or addressing monks.
• Royal Thai - (influenced by Khmer) used when addressing members of the royal family or talking about royalty

Thais living in the countryside and those with less education can usually speak at only the first and second levels, though they will understand the others.

The Thai language is tonal, having 5 tones which distinguish the meanings of words. The five tones are high, rising, middle, falling and low. The Thai language has it's own alphabet, descended from sanskrit, and written from left to right without breaks between the words.

In addition to Standard Thai, Thailand is home to other related Tai languages, including:

• Northern Thai (Lanna, Kam Meuang, or Thai Yuan), in the formerly independent Lanna kingdom (Chiang Mai).
• Isan (Northeastern Thai) is considered by some to be a dialect of the Lao language, which it very closely resembles although written with the Thai alphabet).
• Nyaw language, spoken mostly in Nakhon Phanom province, Sakhon Nakhon province, Udon Thani province of Northeast Thailand.
• Southern Thai (Pak Dtai), spoken about 5 million (1990).
• Galung language, spoken in Nakhon Phanom province of Northeast Thailand.
• Phu Thai, spoken by about 156,000 around Nakhon Phanom province.
• Phuan, spoken by an unknown number of people in central Thailand and Isan.
• Shan (Thai Luang, Tai Long, Thai Yai), spoken by about 56,000 in north-west Thailand along the border with the Shan States of Burma.
• Song, spoken by about 20,000 to 30,000 in central and northern Thailand.
• Thai Dam, spoken by about 20,000 in Isan and Saraburi province.

Many of these languages are spoken by larger numbers outside of Thailand, in neighboring countries. Most speakers of dialects and minority languages speak mainstream Thai as well, since it is the language used in schools and universities all across the kingdom.