Æthelberht (or Ethelbert; Old English: Æþelberht, meaning "magnificent noble") was the King of Kent from 858 and of Wessex from 860 until his death in 865. He was the third son of Æthelwulf of Wessex and his first wife, Osburh. In 855 he became under-king of Kent while his father, Æthelwulf, visited Rome. His brother Æthelbald was left in charge of the West Saxons. After his father's death in 858 he succeeded him as king of Kent and the other eastern parts of the kingdom. When Æthelbald died childless in 860, the kingship of the West Saxons also passed to Æthelberht.
Like his father and brother he was also crowned at Kingston upon Thames. The Anglo-Saxon Chronicle describes Æthelberht's reign as one of good harmony and lasting peace. Though this was true of internal affairs, the Vikings remained a great threat, unsuccessfully storming Winchester and ravaging eastern Kent.
One development was that Wessex and its recent south-eastern conquests became a united kingdom. Unlike his predecessors, Æthelberht did not appoint another member of his family as under-king of Kent. A charter issued in the first year of Æthelberht's reign reflects an extraordinary new kind of assembly: it was the first charter of a West Saxon king to include a full complement both of West Saxon and of Kentish witnesses.
Æthelberht died in 865 and was succeeded by his brother Æthelred. He was buried at Sherborne Abbey in Dorset beside his brother Æthelbald.