Part 1: Unpacking the Puzzle -- 1. Norms, Ideas, and State Policy: A Theoretical Framework -- 2. Key Concepts: Opposing Ideas and Domestic and International Norms in Japan -- Part 2: Japan's Arms Trade Ban Policy -- 3. The Arms Trade Ban Policy during the Cold War: Shared Norm, Different Ideas -- 4. Relaxing the Arms Trade Ban Policy in the Post-Cold War Period: The Influence of International Trends -- Part 3: Japan's Peacekeeping Policy -- 5. Dispatching the Self-Defence Forces in the Cold War Period: Divisive Ideas in Domestic Politics -- 6. The Gulf War and Japan's Participation in United Nations Peacekeeping Operations: The Internalisation of an International Norm -- 7. Japan's Evolving Peacekeeping Policy in the post-Cold War Period: Interaction between Domestic and International Norms -- Part 4: Japan's Evolving Military Roles -- 8. Japan's Expanding Security Roles in the1990s and 2000s: The Emergence of Collective Security -- 9. Peace and Security Legislation: Regulative Effects of a Domestic Norm -- 10. Conclusions