The Norse–Gaels were a people of mixed Gaelic and Norse ancestry and culture. They emerged in the Viking Age, when Vikings who settled in Ireland and in Scotland became Gaelicised and intermarried with Gaels. The Norse–Gaels dominated much of the Irish Sea and Scottish Sea regions from the 9th to 12th centuries. They founded the Kingdom of the Isles, the Kingdom of Dublin, the Lordship of Galloway, and briefly ruled the Kingdom of York. The most powerful Norse–Gaelic dynasty were the Uí Ímair or House of Ivar.

The Norsemen were a North Germanic linguistic group of the Early Middle Ages, during which they spoke the Old Norse language. The language belongs to the North Germanic branch of the Indo-European languages and is the predecessor of the modern Germanic languages of Scandinavia. During the late eighth century, Scandinavians embarked on a large-scale expansion in all directions, giving rise to the Viking Age. In English-language scholarship since the 19th century, Norse seafaring traders, settlers and warriors have commonly been referred to as Vikings. Historians of Anglo-Saxon England distinguish between Norse Vikings (Norsemen) from Norway, who mainly invaded and occupied the islands north and north-west of Britain, as well as Ireland and western Britain, and Danish Vikings, who principally invaded and occupied eastern Britain.