This volume is a collection of some of the most influential essays by Jack Levy on the causes of interstate war. These studies focus on the role of power in the international system, the domestic sources of security policy and war, and the psychology of decision-making. Among the themes uniting all of these studies is that there are patterns in the processes leading to interstate wars, that these patterns are complex, and that an understanding of war requires rigorous theory and that a key prerequisite of theory is conceptual clarity. The focus is on theoretical essays on war and on decision-making in security policy. These essays involve the critique and reconceptualization of major theories of war. For each theory, the author engages in the conceptual clarification of key variables, the identification of the varied causal paths through which each shapes decisions for war and peace, the analytical limitations of the theory, and the methodological hurdles confronting valid empirical tests of the theory. The volume begins with a substantial introductory chapter. Each subsequent chapter begins with a brief introduction, and ends with an annotated bibliographic note that identifies important subsequent work on the topic, and includes a complete set of references. The chapters are organized by a levels-of-analysis framework. It begins with four chapters focusing on power dynamics at the systemic or dyadic levels, including balance of power theory, power transition theory, theories of preventive war, and offense-defense theory. It then turns to the diversionary theory of war, a leading societal-level theory focusing on domestic incentives for adventurous foreign policies. Next are three studies focusing on individual-level, psychological sources of security policy, including misperception, learning, and risk propensity (in the form of prospect theory). The concluding chapter attempts to survey the current state of the art in the study of the causes of interstate war, and identifies some of the major unanswered questions and suggests a number of fruitful paths for future research. This book will be of much interest to students of the causes of war, quantitative methods, war and conflict studies, international relations and security studies.