My dissertation traces the legal and political arguments, as well as the institutional arrangements, that emerged in response to the rise of statelessness as a mass phenomenon from the period after World War I through decolonization. It addresses the question: How did theories of rights, sovereignty, and international law develop in response to the proliferation of people outside the boundaries of international political order? I focus on the way in which the concept of statelessness entered into debates among state officials, legal and political theorists, and within international organizations, over the role of international law in regulating international order and the relationship between citizenship and rights.