The concept of self-defense takes such an important place in the UN Charter and international law. The concept of collective self-defense should also be interpreted and applied within the clear parameters of stated principles of the UN Charter. This is not a concept that can be elastically applied so as to cover a wide range of instances that require military action by like-minded States acting in response to contingent situations. The discussion of collective self-defense within the specific context of Japan at the moment, however, seems to involve issues larger than or beyond the traditional concept of self-defense. Arguably, some aspects of the issues posed seem to fall under the collective security realm which is reserved to the authority of the UN Security Council or which at least requires authorization or delegation from the Security Council. Using the term collective self-defense to address a wide spectrum of military contingencies to be tackled by collective security regime may not square with the provisions of the UN Charter.

I. Introduction
 II. Collective Self-Defense and Collective Security:Two Different Concepts andthe Danger of Mixing them Up
  A. Collective Self-Defense in Article 51 of the UN Charter
  B. Collective Security under the UN Charter
  C. Distinguishing Collective Self-Defense from Collective Security
  D. Confusion Stemming from Mixing up the Two Concepts
 III. Focus on ‘Collective Security’in the Discussions in Japan
  A. Background: The New Defense Guidelines of 2015
  B. Use of Force under the Japanese Constitution
  C. Japan’s Reinterpretation of Article 9 and Broader Military Roles
 IV. Conclusion: Putting Self-Defense Debatesin Their Proper Context

• Jaemin Lee(Seoul National University School of Law)