Causantín or Constantín mac Cináeda (in Modern Gaelic, Còiseam mac Choinnich; died 877) was a king of the Picts. He is often known as Constantine I, in reference to his place in modern lists of kings of Scots, though contemporary sources described Causantín only as a Pictish king. A son of Cináed mac Ailpín ("Kenneth MacAlpin"), he succeeded his uncle Domnall mac Ailpín as Pictish king following the latter's death on 13 April 862. It is likely that Causantín's (Constantine I) reign witnessed increased activity by Vikings, based in Ireland, in Northumbria and in northern Britain. He died fighting one such invasion.