This chapter presents a conceptual framework for explaining SNGs as international actors, drawing principally from International Relations literature. It considers the international activities of SNGs in other countries to provide comparative examples for examining Japanese SNGs. The chapter explains the key developments in Japan’s political and foreign affairs environments, especially post-Cold War, that have enabled and encouraged the emergence of Japanese SNGs as international actors. The general theoretical assumption of mainstream International Relations theories is that even after the Cold War, the world is still comprised of nations represented officially only by a unitary national government whose mandate and responsibility align with the nation’s border. Trade, investment and other economic relations pursued by SNGs with partners overseas are the most common and least controversial aspect of SNG involvement in foreign affairs.