 The phrase " Northern Isles " generally refers to the main islands of the Orkney and Shetland archipelagos . Stroma , which lies between mainland Scotland and Orkney , is part of Caithness , and so falls under Highland council area for local government purposes , not Orkney . It is , however , clearly one of the " northern isles " of Scotland . Fair Isle and Foula are outliers of Shetland , but would normally be considered as part of Shetland and thus the Northern Isles . Similarly , Sule Skerry and Sule Stack , although distant from the main group , are part of Orkney and technically amongst the Northern Isles . However , the other small islands that lie off the north coast of Scotland are in Highland and thus not usually considered to be part of the Northern Isles . 
