Oliver Cromwell's expedition to Ireland in 1649 is understandably something that historians take a lot of interest in. Partly because it has become a contentious event in Irish history, partly because it saw the eventual reunification of two of the three Stuart Kingdoms under Parliament at the end of the Civil War. Dr Siochru's book is an interesting addition to the scholarship on the subject- but it has major problems. On the positive side though what he has done is provide a readable straightforward account of Irish politics in the 1640s and 1650s. Few historians would challenge many of the conclusions here about the horrors of war in Ireland, about the position of the royalist Catholic alliance who opposed Cromwell and fortified the larger towns within Ireland and about the importance of logistics in supporting Cromwell's victories. However the title to the book is misleading: this is not really about Cromwell's invasion of Ireland- indeed the author's interpretation of major documents written by Cromwell like the Clonmacnoise Declaration differs from that of distinguished academics like John Morrill- rather it is really about how the Royalists and Catholics reacted to the invasion. In this sense it continues the author's previous work on the Confederation of Kilkenny. The most valuable sections of the book concentrate on the relations amongst the royalist command- between Ormond, his deputy Clanrickard and various other peers, bishops and commanders. Siochru does not delve into the same issues on the Parliamentary side- Ormond and Clanrickard are fleshed out more than Cromwell and Ireton: a minor commander like Hugh Dubh O'Neill more than his equivalent, Colonel Reynolds or Sir Charles Coote on the Parliamentary side. There is nothing wrong with that- but it means that the book is mistitled. An account of the ideology and politics of the Parliamentarian side (despite article and lecture contributions by Sarah Barber and John Morrill) remains to be written. We all know the army were anti-Catholic, that Cromwell authorised atrocities and lost control of his troops, what we are less clear about is the kind of regime Cromwell and his allies wanted to create in Ireland and how that related to their vision of what they wanted to do in England. Siochru shows us how the Catholics and royalists reacted to this event- a valuable contribution- but not quite the one one would expect from a book entitled God's executioner, Oliver Cromwell and the conquest of Ireland!