Northumbria (Old English: Norþanhymbra / Norþhymbre) was a mediæval kingdom of the Angles, in what is now Northern England and South-East Scotland, becoming subsequently an earldom in a united Anglo-Saxon kingdom of England. The name reflects the approximate southern limit to the kingdom's territory, the Humber Estuary.

Northumbria was formed by Æthelfrith in central Great Britain in Anglo-Saxon times. At the beginning of the 7th century the two kingdoms of Bernicia and Deira were unified. (In the 12th century writings of Henry of Huntingdon the kingdom was defined as one of the Heptarchy of Anglo-Saxon kingdoms.) At its greatest the kingdom extended at least from just south of the Humber, to the River Mersey and to the Forth (roughly, Sheffield to Runcorn to Edinburgh) – and there is some evidence that it may have been much greater (see map).

The later (and smaller) earldom came about when the southern part of Northumbria (ex-Deira) was lost to the Danelaw. The northern part (ex-Bernicia) at first retained its status as a kingdom but when it become subordinate to the Danish kingdom it had its powers curtailed to that of an earldom, and retained that status when England was reunited by the Wessex-led reconquest of the Danelaw. The earldom was bounded by the River Tees in the south and the River Tweed in the north (broadly similar to the modern North East England).