This course offers a comprehensive survey of topics in international security and prepares students to conduct original research in this field. The course covers a broad range of security challenges: interstate war, nuclear deterrence, coercive diplomacy, alliance formation, arms control, civil war, and the proliferation of weapons of mass destruction. The course is organized around key debates in the field: Does backing down in a crisis invite further aggression, or do adversaries assess each threat in isolation? Are nuclear weapons effective in compelling adversaries, or are they only good at deterring attacks? Why is arms control so rare, and when does it constrain adversaries? Is unipolarity good for global order, or does it generate its own conflict dynamics? Can military alliances mitigate the risk of conflict, or do they increase it? Along with these debates, a structured series of assignments helps students learn how to identify puzzles in existing literature, formulate analytical research questions, develop coherent theoretical arguments, and test their empirical implications. By the end of the course, students will have a thorough understanding of key theoretical and policy debates in international security and will complete an original research paper.