Vikings plagued the coasts of Ireland and Britain in the 790s. By the mid-ninth century vikings had established a number of settlements in Ireland and Britain and had become heavily involved with local politics. A particularly successful viking leader named Ivarr campaigned on both sides of the Irish Sea in the 860s. His descendants dominated the major seaports of Ireland and challenged the power of kings in Britain during the later ninth and tenth centuries. This book provides a political analysis of the deeds of Ivarr's family from their first appearance in Insular records down to the year 1014. Such an account is necessary in light of the flurry of new work that has been done in other areas of Viking Studies. In line with these developments Clare Downham provides a reconsideration of events based on contemporary written accounts.