The religious beliefs and practices of the ancient Celts, an ancient Indo-European people. In the 4th century BCE their influence and territories covered the length of Europe, stretching from Britain to Asia Minor. Celtic mythology consists of three groups:
- The Goidelic, including Ireland, the Isle of Man, and the western highlands of Scotland. In language, race, and tradition these form a homogenous block;
- The Insular Brythonic, including Wales and Cornwall, also inhabited by kindred people with a somewhat similar history;
- The Continental Brythonic, that is, Brittany. Though racially akin to the Welsh and Cornish, the Bretons have had a very differently history and enjoy a distinct culture.