OUR UNIPOLAR WORLD IS PASSING INTO HISTORY, AS THE ECONOMIC CENTER OF gravity shifts eastward and southward and new centers of power emerge. Our international governance systems and institutions, constructed out of the ruins of World War II and the Great Depression, have been steadily lagging the steepening curve of change. Meanwhile, as the world struggles with the aftershocks of the global financial and economic crisis, terrorism, transnational crime and drug trafficking, climate change, food security and energy prices, the Arab Awakening, Japan's triple crises, failing and fragile states, the dangers of nuclear proliferation, and so forth, the virtues of multilateral cooperation are being rediscovered. Many see renewed merit in pooling national sovereignty in cooperative institutional arrangements. (1) At the same time, the preeminent power in the international system, the United States, burdened by debt, hobbled by internal divisions, newly conscious of its limits, led by a president whose formative years are more North-South than East-West, is itself putting greater stock in partnership and multilateral cooperation. (2) In response to this unprecedented pace and scope of change, old institutions are innovating and new forms and varieties of international cooperation are being called into being. Issues of legitimacy, accountability, social justice, and effectiveness are generating calls for change. Some, especially the emerging powers such as India, Brazil, and China would like to see a better representation of Southern values and interests in global summitry and in the major decisionmaking organs of the United Nations and Bretton Woods system. Western powers in the North privilege increased effectiveness. Still others, including the increasingly mobilized voices of civil society, want to see more accountability of the powerful to the less powerful, nationally and internationally, North and South. These continuing variances in what forms of cooperation are desirable pose formidable governance challenges.