Is a global institutional order composed of sovereign states fit for cosmopolitan moral purpose? Cosmopolitan political theorists challenge claims that states, nations or other collectives have ultimate moral significance. They focus instead on individuals: on what they share and on what each may owe to all the others. They see principles of distributive justice - and increasingly political justice - applying with force in a global system in which billions continue to suffer from severe poverty and deprivation, political repression, interstate violence and other ills. Cosmopolitans diverge widely, however, on the institutional implications of their shared moral view. Some argue that the current system of competing sovereign states tends to promote unjust outcomes and stands in need of deep structural reform. Others reject such claims and contend that justice can be pursued through transforming the orientations and conduct of individual and collective agents, especially states. This volume brings together prominent political theorists and International Relations scholars -- including some skeptics of cosmopolitanism -- in a far-ranging dialogue about the institutional implications of the cosmopolitan approach. Contributors offer penetrating analyses of both continuing and emerging issues around state sovereignty, democratic autonomy and accountability, and the promotion and protection of human rights. They also debate potential reforms of the current global system, from the transformation of cities and states to the creation of some encompassing world government capable of effectively promoting cosmopolitan aims.