Solving the puzzle of war has dominated the attention of scholars and policy makers alike for decades. The new edition of What Do We Know about War? gauges the knowledge ascertained about the causes of war and the conditions of peace by the scientific community since the publication of the first edition, more than twenty years ago. In addition, it provides insights into new areas of research and concludes with reflections on what we have learned. This book is an essential read for academics, policy makers, and students interested in questions of war and peace.