The historical Celts were a diverse group of tribal societies in Iron Age Europe. The Celts expanded over a wide range of lands: as far west as Ireland and the Iberian Peninsula, as far east as Galatia (central Anatolia), and as far north as Scotland.

Today, the term ‘Celtic’ is generally used to describe the languages and respective cultures of Ireland, Scotland, Wales, Cornwall, the Isle of Man and Brittany, also known as the Six Celtic Nations. These are the regions where four Celtic languages are still spoken to some extent as mother tongues: Irish Gaelic, Scottish Gaelic, Welsh, and Breton plus two recent revivals, Cornish and Manx.