The Northern Thai language is the language of the people of Lannathai, Thailand. It is a Tai language, related to Thai and Lao. Northern Thai has approximately six million speakers, most of whom live in Thailand, with a few thousand in Laos.

Speakers of this language generally consider the name Yuan to be pejorative. They generally call themselves Khon Mueang (or Lannathai, or Northern Thai--or Western Lao, across the border). The language is generally known by one of these terms, or as Phayap. The term Yuan is still used for the distinctive Lannathai script, which is closely related to the old Thai Lue alphabet and the Lao religious alphabets. It also resembles the Burmese and Mon alphabets. (All these alphabets derive from the Old Mon alphabet.) The use of the tua mueang, as the traditional alphabet is known, is now largely limited to Buddhist temples, where many old sermon mansuscripts are still in active use. There is no active production of literature in the traditional alphabet.

Most linguists consider Northern Thai to be more closely related to Thai and the other Chiang Saeng languages than to Lao and the Lao-Phutai languages, but the distinction is never easy to make, as the languages form a continuum with few sharp dividing lines.

See also: Thai Yuan