The extinct Dacian language may have developed from Proto-Indo-European (PIE) in the Carpathian region around 2,500 BC and probably died out by AD 600. In the 1st century AD, it was the predominant language of the ancient regions of Dacia, probably Moesia and possibly of some surrounding regions. It belonged to the Indo-European language family. The available evidence, which is scarce, suggests that the Dacian language might have belonged to the satem group of the Indo-European (IE) languages.

Dacian is considered by some scholars e.g. Baldi (1983) and Trask (2000), to be a dialect of the Thracian language, or vice versa; the term Daco-Thracian, or Thraco-Dacian, is used by linguists to denote such a common language, or its presumed parent-branch of Indo-European. It is alternatively considered to be a language separate from Thracian but related to it and to Phrygian; or a language unrelated to either Thracian or Phrygian, except in the distant sense of sharing an Indo-European origin, as was theorised by Vladimir Georgiev in 1977.