The Britons (sometimes Brythons or British) were the Celtic people culturally dominating Great Britain from the Iron Age until the Early Middle Ages. They spoke the Insular Celtic language known as British or Brythonic. They lived throughout Britain south of about the Firth of Forth; after the 5th century Britons also migrated to continental Europe, where they established the settlements of Brittany in France and the obscure Britonia in what is now Galicia, Spain. Their relationship to the Picts north of the Forth has been the subject of much discussion, though most scholars accept that the Pictish language during this time was a Brythonic language related to, but perhaps distinct from, British.

The earliest evidence for the Britons and their language in historical sources dates to the Iron Age. After the Roman conquest of 43 AD, a Romano-British culture began to emerge. With the advent of the Anglo-Saxon settlement in the 5th century, however, the culture and language of the Britons began to fragment. By the 11th century their descendants had split into distinct groups, and are generally discussed separately as the Welsh, Cornish, Bretons, and the people of the Hen Ogledd ("Old North"). The British language developed into the distinct branches of Welsh, Cornish, Breton, and Cumbric.