The Sluagh (Irish: (ˈsˠl̪ˠuə), Scottish Gaelic: (ˈs̪l̪ˠuəɣ); Old Irish: slúag; English: 'host, army, crowd'), or Sluagh na marbh ('host of the dead'), were the hosts of the unforgiven dead in Irish and Scottish folklore. In the words of British folklorist Lewis Spence, "In the Western Isles of Scotland the Sluagh, or fairy host, was regarded as composed of the souls of the dead flying through the air, and the feast of the dead at Hallowe'en was likewise the festival of the fairies."

Usually taking a crescent form, similar to a flight of grey birds, they were said to be able to approach and pick up a person from any direction and then transport them far away through the air, from one island to another. Although they could sometimes rescue humans from dangerous rock clefts, they were generally portrayed as dangerous to mortals.