The settlement of Iceland (Icelandic: landnámsöld [ˈlantˌnaumsˌœlt]) is generally believed to have begun in the second half of the ninth century, when Norse settlers migrated across the North Atlantic. The reasons for the migration are uncertain: later in the Middle Ages Icelanders themselves tended to cite civil strife brought about by the ambitions of the Norwegian king Harald I of Norway, but modern historians focus on deeper factors, such as a shortage of arable land in Scandinavia. Unlike Great Britain and Ireland, Iceland was unsettled land and could be claimed without conflict with existing inhabitants.
On the basis of Íslendingabók by Ari Þorgilsson, and Landnámabók, histories dating from the twelfth and thirteenth centuries and providing a wealth of detail about the settlement, the years 870 and 874 have traditionally been considered the first years of settlement. However, these sources are largely unreliable in the details they provide about the settlement, and recent research focuses more heavily on archaeological and genetic evidence.