We confront daunting twenty-first century challenges hobbled by twentieth century institutions. In a world ever more interdependent, deepening global-scale risks—climate change, financial instability, terrorism, to name a few—threaten the planetary commonwealth, even the continuity of civilization. Yet coherent and timely responses lie beyond the grasp of our myopic and disputatious state-centric political order. Closing this perilous gap between obsolete geopolitics and emerging geo-realities delineates an urgent political endeavor: constructing a legitimate and effective system of world governance. Key steps on that path involve reforming the United Nations and nurturing new venues for the meaningful exercise of global citizenship.