Do national boundaries have fundamental moral significance, or do we have moral obligations to foreigners that are equal to our obligations to our compatriots? The latter position is known as cosmopolitanism, and this volume brings together a number of distinguished political philosophers and theorists to explore cosmopolitanism and the positive arguments that can be made for it. Their essays provide a comprehensive overview of the current state of the debate as well as the alternative visions of cosmopolitanism that will interest a wide range of readers in philosophy, political theory, and law.