Aldfrith (died 14 December 704 or 705) sometimes Aldfrid, Aldfridus (Latin), or Flann Fína mac Ossu (Classical Irish), is king of Northumbria from 685 until his death.

He is described by early writers such as Bede, Alcuin and Stephen of Ripon as a man of great learning.

Some of his works and some letters written to him survive.

His reign is relatively peaceful, marred only by disputes with Bishop Wilfrid, a major figure in the early Northumbrian church.

Aldfrith was born on an uncertain date to Oswiu of Northumbria and an Irish princess named Fín.

Oswiu later becomes King of Northumbria; he dies in 670 and is succeeded by his son Ecgfrith.

Aldfrith is educated for a career in the church and becomes a scholar.

However, in 685, when Ecgfrith is killed at the battle of Nechtansmere, Aldfrith is recalled to Northumbria, reportedly from the Hebridean island of Iona, and becomes king.

In his early-eighth-century account of Aldfrith's reign, Bede states that he "ably restored the shattered fortunes of the kingdom, though within smaller boundaries".

His reign sees the creation of works of Hiberno-Saxon art such as the Lindisfarne Gospels and the Codex Amiatinus, and is often seen as the start of Northumbria's golden age.