The Caledonians or the Caledonian Confederacy were a Brittonic-speaking (Celtic) tribal confederacy in what is now Scotland during the Iron Age and Roman eras. The Greek form of the tribal name gave rise to the name Caledonia for their territory. The Caledonians were considered to be a group of Britons, but later, after the Roman conquest of the southern half of Britain, the northern inhabitants were distinguished as Picts, thought to be a related people who would have also spoken a Brittonic language. The Caledonian Britons were thus enemies of the Roman Empire, which was the state then administering most of Great Britain as the Roman province of Britannia.

The Insular Celts were speakers of the Insular Celtic languages in the British Isles and Brittany. The term is mostly used for the Celtic peoples of the isles up until the early Middle Ages, covering the British–Irish Iron Age, Roman Britain and Sub-Roman Britain. They included the Celtic Britons, the Picts, and the Gaels.