Expanding upon the normative position of co-progressiveness elaborated in Towards an International Law of Co-progressiveness (Martinus Nijhoff, 2004), this volume explores membership, leadership, and responsibility in the international system and how these matters reflect and inform international law. Issues discussed include: (1) the recognition and role of States, civilizations, and regions in the international system and how these entities are influenced by factors such as declarations of independence, intrinsic and instrumental values, diversity, and public opinion; (2) the distribution of power among States, its legitimacy, and the consequent influence this distribution has on the international system and world politics; and (3) member responsibility for acts of international organizations as well as the possibility of establishing and enforcing universal jurisdiction as a tool for implementing responsibility across the world.