The Tai–Kadai languages, also known as Kra–Dai, Daic, and Kadai, are a language family of highly tonal languages found in southern China, northeast India and Southeast Asia. They include Thai and Lao, the national languages of Thailand and Laos respectively. Around 93 million people speak Tai-Kadai languages, 60% of whom speak Thai.Ethnologue lists 95 languages in this family, with 62 of these being in the Tai branch.

The diversity of the Tai–Kadai languages in southern China, especially in Guizhou and Hainan, suggests that this is close to their homeland. The Tai branch moved south into Southeast Asia only about a thousand years ago, founding the nations that later became Thailand and Laos in what had been Austroasiatic territory.

The name "Tai–Kadai" is controversial, and arguments have been made that it should be replaced. The name comes from an obsolete bifurcation of the family into two branches, Tai and Kadai (all else). Yet the name Kadai suggests that it includes Tai, and as such is sometimes used to refer to the entire family. On the other hand, some references restrict the usage of "Kadai" to the Kra branch of the family, for which the name Kra suffices. The replacement name Kra–Dai has been suggested, as Kra and Dai are two large and well-established subgroups that are on different sides of a major historical split. The name Kra–Dai has since been adopted in several major scholarly works on the family.

Tai–Kadai consists of five well established branches, Hlai, Kra, Kam–Sui, Tai, and the Ong Be language:

In 1942, Paul K. Benedict placed three Kra languages (Gelao, Laqua and Lachi) together with Hlai in a group for which he coined the name "Kadai", from ka meaning "person" in Gelao and Laqua, and Dai, a form of a Hlai autonym. He further proposed a genetic grouping of Tai, Kadai and Malayo-Polynesian.

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