Donald II of Scotland (Domnall mac Causantín) was king of Scotland from 889 to 900. He was the son of King Constantine I and first cousin of the previous king Eochaid and of his successor Constantine II.

Donald took the throne of Scotland in battle as an act of revenge. King Giric I of Scotland (who ruled jointly with Donald's predecessor, Eochaid) had murdered Donald's uncle, Aed, in 878. Upon Giric's death, Donald expelled Eochaid from the country, thereby taking rulership of Scotland for himself.

It was under the rule of King Donald II that the British kingdom of Strathclyde came under Scottish dominance to create the Kingdom of Alba, thus being recognized in the Annals of Ulster as "ri Alban" as opposed to "rex Pixtorum," as his predecessors had been known. His reign coincided with renewed invasions by the Danes, who came less to plunder and more to occupy the lands bordering Scotland and the Anglo-Saxon kingdoms. The Danish had conquered all of northern Scotland through the leadership of 'Sigurd the Mighty'. Donald was also embroiled in efforts to reduce the Highland robber tribes.

Details of his death are obscure and uncertain. By one account he was slain at Dunnottar while meeting a Danish invasion; by another he died of infirmity brought on by his campaigns against the Highlanders, a natural death that is very uncommon in this period. He was buried on the Isle of Iona, the historic resting place of all Dalriadan and early Scottish kings. He was succeeded by his cousin Constantine II. His son, Malcolm, later became King Malcolm I of Scotland.