The creation of new frameworks for global governance will be a defining challenge for the twenty-first century world, and the attitude of the United States will be among the most important factors in determining the shape and stability of the world order that results from these efforts. The need for a reformed, robust system of multilateral cooperation has never been more obvious. Today’s global agenda is dominated by a host of issues—from terrorism to climate change to the proliferation of weapons of mass destruction—that no single country, no matter how powerful, can address on its own. Tomorrow’s challenges and policy agendas will only be more transnational in scope. At the same time, existing multilateral institutions are increasingly divorced from global realities, hindering their capacity to deliver global public goods and mitigate global “bad.” Since the end of the Cold War, world politics have been transformed in fundamental ways.