Welsh is a Celtic language of the Brittonic subgroup that is native to the Welsh people. Welsh is spoken natively in Wales, by some in England, and in Y Wladfa.

The Celts or Celtic peoples were a collection of Indo-European peoples in Europe and Anatolia, identified by their use of Celtic languages and other cultural similarities. Major Celtic groups included the Gauls; the Celtiberians and Gallaeci of Iberia; the Britons, Picts, and Gaels of Britain and Ireland; the Boii; and the Galatians. The relation between ethnicity, language and culture in the Celtic world is unclear and debated; for example over the ways in which the Iron Age people of Britain and Ireland should be called Celts. In current scholarship, 'Celt' primarily refers to 'speakers of Celtic languages' rather than to a single ethnic group.