The Thai people, or formerly Siamese, are the main ethnic group of Thailand and are part of the larger Tai ethnolinguistic peoples found in Thailand and adjacent countries in Southeast Asia as well as southern China. Their language is the Thai language, which is classified as part of the Tai_Kadai family of languages, and the majority of Thai are followers of Theravada Buddhism. The term Thai people may also refer to the population of Thailand in general, and not only to ethnic Thais. Today, "Thai people" usually includes Central and Southern Thai (Siamese proper), Northern Thai (Lanna) and Isan people (strictly speaking Western Lao). There have been many theories proposing the origin of the Tai people, of which the Thai are a subgroup. Especially the association of the Tai people with the Kingdom of Nanzhao that has been proved to be invalid.
Contributions by Boing! said Zebedee, KLL Joe, and Khoikhoi.