This book has advice for future United Nations peace operations, but it also marks the end of widespread optimism about what the UN could achieve if it moved beyond merely monitoring cease-fire lines between states and instead tackled the problems caused by vicious fighting within states. The authors address the familiar case studies (including Cambodia, Somalia, East Timor, and the former Yugoslavia) but do so within an unusually sophisticated theoretical framework, based on a thorough analysis of the literature on the causes and conduct of civil wars. They conclude that the deeper the underlying hostility and the shallower the residual state capacity in the affected country, the greater the international effort required for any successful peace building. Beyond that, the key message is that there is no formula guaranteeing success and that the UN is much better at picking up the pieces after a war than at intervening in an ongoing conflict. This is all valuable as far as it goes, but the book lacks a sense of the changing international context, with no mention, for example, of the role of Islamist groups in civil wars.