Constantine, son of Áed (Medieval Gaelic: Constantín mac Áeda; Modern Gaelic: Còiseam mac Aoidh, known in most modern regnal lists as Constantine II; before 879–952) was an early King of Scotland, known then by the Gaelic name Alba. The Kingdom of Alba, a name which first appears in Constantine's lifetime, was in northern Great Britain. The core of the kingdom was formed by the lands around the River Tay. Its southern limit was the River Forth, northwards it extended towards the Moray Firth and perhaps to Caithness, while its western limits are uncertain. Constantine's grandfather Kenneth I of Scotland (Cináed mac Ailpín, died 858) was the first of the family recorded as a king, but as king of the Picts. This change of title, from king of the Picts to king of Alba, is part of a broader transformation of Pictland and the origins of the Kingdom of Alba are traced to Constantine's lifetime.
His reign, like those of his predecessors, was dominated by the actions of Viking rulers in Britain and Ireland, particularly the Uí Ímair ("the grandsons of Ímar", or Ivar the Boneless). During Constantine's reign the rulers of the southern kingdoms of Wessex and Mercia, later the Kingdom of England, extended their authority northwards into the disputed kingdoms of Northumbria. At first allied with the southern rulers against the Vikings, Constantine in time came into conflict with them.