Deira is a kingdom in Northern England that probably emerged when Anglian warriors conquered the Derwent Valley in the third quarter of the fifth century.

It extends from the Humber to the Tees, and from the sea to the western edge of the Vale of York.

It is the southern of the two kingdoms of Deira and Bernicia which later merge to form the kingdom of Northumbria.The name of the kingdom is of Brythonic origin, perhaps from Deifr, meaning "waters", or from Daru, meaning "oak", in which case it would mean "the people of the Derwent", a derivation also found in the Latin name for Malton, Derventio.

According to Simeon of Durham (writing early in the 12th century) it extended from the Humber to the Tyne, but the land was waste north of the Tees.

After the Brythonic kingdom centered around Eboracum, which may have been called Ebrauc, is taken by King Edwin, the city of Eboracum becomes its capital and is called Eoforwic ("boar-place") by the Angles.

The first Anglian king of Deira of whom we have any record is Ælla, who flourishes in the later 6th century after conquering the realm from the Britons in 581.

After his death, Deira is subject to king Æthelfrith of Bernicia, who unites the two kingdoms into Northumbria.

Æthelfrith rules until the accession of Ælla's son Edwin, in 616 or 617, who also rules both kingdoms until 633.Osric, the nephew of Edwin, rules Deira after Edwin, but his son Oswine is put to death by Oswiu in 651.

For a few years subsequently Deira is governed by Æthelwald son of Oswald of Bernicia.Bede wrote of Deira in his Historia Ecclesiastica (completed in 731).