A revised and expanded second edition of a classic work on the history of early medieval Ireland c.800 to the coming of the Normans, first published in 1972. It deals with the geography of power, kingship and society, the church and its structures, the Viking wars, the twelfth-century reform and the wars of the Irish dynasties, 950-1169. With a new bibliography and up-to-date references and notes.The book presents an original assessment of the changing structure of Irish society in the period of the Viking wars and beyond -- a period of violent change in some aspects but one of extraordinary continuity in others. The most interesting developments -- the simplication of Irish class structure, the emergence of a new monarchy based on farflung dynasties, and the reform of the Irish church and the growth of institutions -- are treated in detail.