International relations often seems chaotic, complex, and difficult to understand. Theoretical explanations can help resolve this confusion, but for much of the modern history of international relations, theory has often been vague or highly general. This 4-volume work provides the definitive resource on middle-range theory in the widest survey of empirical IR theory ever conducted. Through over 150 entries by leading scholars, The Oxford Encyclopedia of Empirical International Relations Theory provides an authoritative overview of the central approaches, methodologies, and topics of the field. Its comprehensive examination of both classic and emerging theories underscores the breadth and depth of international relations theory today and is a necessary resource for students and as well as both new and established scholars.