This book offers a comprehensive moral theory of privatization in war. It examines the kind of wars that private actors might wage separate from the state and the kind of wars that private actors might wage as functionaries of the state. The first type of war serves to probe the ad bellum question of whether private actors can justifiably authorize war, while the second type of war serves to probe the in bello question of whether private actors can justifiably participate in war. The cases that drive the analysis are drawn from the rich and complicated history of private military action, stretching back centuries to the Italian city-states whose mercenaries were reviled by Machiavelli. The book also takes up the hypothetical examples conjured by philosophers—the private protective agencies of Robert Nozick’s Anarchy, State, and Utopia, for example, and the private armies of Thomas More’s Utopia. The aim of this book is to propose a theory of privatization that retains currency not only in assessing current military engagements, but past and future ones as well. In doing so, it also raises a set of important questions about the very enterprise of war. This book will be of much interest to students of ethics, political philosophy, military studies, international relations, war and conflict studies, and security studies.