The Ayutthaya Kingdom or the Empire of Ayutthaya was a Mon and later Siamese kingdom that existed in Southeast Asia from 1351 to 1767, centered around the city of Ayutthaya, in Siam, or present-day Thailand. European travellers in the early 16th century called Ayutthaya one of the three great powers of Asia. The Ayutthaya Kingdom is considered to be the precursor of modern Thailand, and its developments are an important part of the history of Thailand.

Thai people, Chao Phraya Thai, Central Thai people, Southern Thai people, Siamese, Thai Siam, Tai Noi people, are a Southeast Asian ethnic group native to Thailand. In a narrower sense, the Thais are also a Tai ethnic group dominant in Central and Southern Thailand. Part of the larger Tai ethno-linguistic group native to Southeast Asia as well as Southern China and Northeast India, Thais speak the Sukhothai languages, which is classified as part of the Kra–Dai family of languages. The majority of Thais are followers of Theravada Buddhism.