Tai peoples are anybody predominantly descended from the original proto-Tai speakers. This includes those who have Tai blood but no longer speak Tai languages, some 8-10 million people in Northeastern India (not limited to Assam) claim descent from Ahomese, but may have intermarried with others and now speak Assamese, another tens of thousands in India still use Tai languages (mostly in Arunachal Pradesh). Aside from India, where language has eroded, Tai groups can be traced through their language.

Today, Tai peoples are split among nations, leading to different names for them. In China, Tai peoples (excluding Rauz peoples) are lumped together as Dai people, despite not self-identifying as "Dai", and in Burma they're similarly lumped together as Shan people (again, a bureaucratic designation not ethnic self-identity), in Vietnam Tay, and Laos Lao, and Thailand Thai people.

In a paper published in 2004, Linguist Laurent Sagart hypothesized that the proto-Tai–Kadai language originated as an Austronesian languages that migrants carried from Taiwan to mainland China. Afterwards, the language was then heavily influenced by local languages from Sino-Tibetan, Hmong–Mien, or other families, borrowing much vocabulary and converging typologically. Much closer to the present, some peoples speaking Tai languages migrated southward over the mountains into Southeast Asia, perhaps prompted by the coming of the Han Chinese to south China.