Vikings plagued the coasts of Ireland and Britain in the 790s. Over time, their raids became more intense and 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 Aivarr 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. In 1014, the battle of Clontarf marked a famous stage in the decline of viking power in Ireland whilst the conquest of England in 1013 by the Danish king Sveinn Forkbeard marked a watershed in the history of vikings in Britain.The descendants of Aivarr continued to play a significant role in the history of Dublin and the Hebrides until the twelfth century, but they did not threaten to overwhelm the major kingships of Britain or Ireland in this later period as they had done before. This book provides a political analysis of the deeds of Aivarr'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.Recent theoretical approaches to the subject have raised many interesting questions regarding identity, material culture and structures of authority. Archaeological finds and excavations have also offered potentially radical insights into viking settlement and society. In line with these developments Clare Downham provides a reconsideration of events based on contemporary written accounts. It will appeal to a wide range of people who are curious to know more about the history of vikings in Britain and Ireland.