This textbook presents security studies as a branch of international relations theory, providing readers with the critical conceptual tools to develop their expertise. The author evaluates the claims of rival theories - realism, neorealism, liberal institutionalism, classical economic liberalism, and Marxism - to explain why international actors choose or eschew force and coercive threats in order to elicit favorable outcomes in their interdependent exchanges. Also discussed are behaviorism and constructivism, contesting approaches to validate prevailing security paradigms. The author argues that only an interdisciplinary approach to security, drawing on the insights of each perspective, can meet the rigorous requirements of testable theory and the practical needs of actors in an increasingly globalizing world. The book will provide students and scholars of international relations and security studies with a valuable survey of the subject, and includes essay questions and guides to further reading.