Andrew Louth's book is part of a series, of which the preceding and following volumes appeared in 1989 and 1994 respectively; the author took over the editorship of the series from the late eminent Orthodox scholar John Meyendorff and his own book admirably fills the existing chronological gap. Louth has taught Byzantine theology and patristics at Durham and before that at Goldsmiths' College in London, and is himself Orthodox and ordained. As its start and end dates indicate (the Sixth Ecumenical Council in ad 680–1 at one extreme and the battle of Manzikert and the loss of Bari to the Normans at the other), this book is written more from the eastern perspective; this is justified by the author on the grounds that the emphasis is more often the other way round. In fact he has produced a clear and very helpful comparative guide to the development of the Church in both east and west, pointing to several apparent convergences at particular periods. This is not a prehistory of the ‘Great Schism’; on the contrary, Louth is at pains to emphasise both that the events of ad 1054 were not perceived on either side at the time as a major break, and that there was no inexorable process leading to such a break. Instead, there were many similarities and many connections between east and west, and the very issues that loomed so large in later periods, such as the western use of unleavened bread in the eucharist and insistence on the celibacy of the clergy, assumed major importance for particular reasons in the eleventh century rather than out of some inevitable prior process. Louth writes clearly and well, with helpful explanations of issues such as the growth of claims to papal authority and the role of the patriarch in Byzantium, and he is a good guide to many new areas in recent scholarship. He is often cautious in giving explanations where evidence is lacking, and tends overall to see ecclesiastical developments as taking place in the context of general political change. This is not a social history of Christianity, whether in east or west; it focuses instead on structures and, in places, on the leading personalities and their writings. He is himself the author of important books on the seventh and eighth-century theologians Maximus Confessor and John of Damascus, and his defence in this book of the controversial eleventh-century writer Michael Psellos against recent rationalising interpretations is also particularly interesting. Similarly, he is not afraid to describe most current approaches to the importance attached to icons in Byzantium as a caricature. The choice of ad 1071 as the end point runs the risk of imposing a narrative of inevitability, and the last chapter is indeed entitled (misleadingly in my view) ‘Turks, Normans and the collapse of the Byzantine empire’. But in general this is a fine, and often astringent, guide to a wide range of highly complex developments which are all too often presented in very tendentious terms.