 The 8th century was also the time the Viking invasions of the Scottish seaboard commenced and with them came the arrival of a new culture and language for the Northern Isles , the fate of the existing indigenous population being uncertain . According to the Orkneyinga Saga , Vikings then made the islands the headquarters of pirate expeditions carried out against Norway and the coasts of mainland Scotland . In response , Norwegian king Harald Hårfagre ( " Harald Fair Hair " ) annexed the Northern Isles in 875 and Rognvald Eysteinsson received Orkney and Shetland from Harald as an earldom as reparation for the death of his son in battle in Scotland . ( Some scholars believe that this story is apocryphal and based on the later voyages of Magnus Barelegs . ) 
