The Celtic languages are a branch of the Indo-European language family. They are divided into four groups:
- Hispano-Celtic: Celtiberian, perhaps also Lusitanian and Tartessian if these are Celtic at all
- Gaulish with Lepontic and Galatian
- Brythonic (British): Welsh, Cornish, Breton
- Goidelic: Irish, Manx, Scots Gaelic
Only the last two groups (Insular Celtic) are still spoken today. The others (Continental Celtic) have been extinct since antiquity. The Insular Celtic languages show some typologically interesting features such as VSO word order and initial mutations that are not found in any other group of Indo-European languages, not even in the Continental Celtic languages.
The Celtic languages have inspired several conlangers to create Celtic and Celtic-influenced conlangs.