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.