By the middle of the 5th century the Roman Empire in North-West Europe was at an end, and the disappearance of Imperial power allowed people from outside the Empire's borders to move into Western Europe. One of the latest of these 'Dark Age' folk movements was from Scandinavia.

The Old Norse word Viking meant a pirate. The earliest sea-borne expeditions of the Pagan Norsemen (from Denmark and Sweden as well as Norway, and starting at the end of the 8th century) were essentially violent raids for booty. The attacks on Christian monasteries in the British Isles gave the North men a fearsome reputation. Soon settlers and traders followed the raiders; flourishing towns grew up in places like York and Dublin.

The Vikings settled in the Northern and Western Isles of Scotland, and areas of the mainland, especially Caithness and Sutherland, and parts of Galloway and Argyll. The Norse period can be identified from a study of settlement sites (e.g. Jarlshof in Shetland), graves and deposited hoards of silver. By the mid 13th century Norse influence had waned, though Orkney and Shetland only became part of Scotland in 1469.

The Orkney and Shetland Isles, easily reached by sea from Scandinavia, provided secure bases for the Norsemen who settled there in great strength from about AD 800 onwards. The language of the earlier inhabitants, presumably part pictish and part aboriginal, disappeared for centuries and a language descended from Old Norse was still being spoken in Shetland in the 19th century.