Maccus mac Arailt (fl. 971–974), or Maccus Haraldsson, was a tenth-century King of the Isles. Although his parentage is uncertain, surviving evidence suggests that he was the son of Harald Sigtryggson, also known as Aralt mac Sitriuc, the Hiberno-Norse King of Limerick. Maccus' family is known as the Meic Arailt kindred. He and his brother, Gofraid, are first recorded in the 970s. It was during this decade and the next that they conducted military operations against the Welsh of Anglesey, apparently taking advantage of dynastic strife within the Kingdom of Gwynedd.