The two traditional ways of thinking about justice at the global level either limit the applicability of justice to states or else extend it to all human beings. The view I defend rejects both these approaches and instead recognizes different considerations or conditions based on which individuals are in the scope of different principles of justice. Finding a philosophically convincing alternative to those approaches strikes me as the most demanding and important challenge contemporary political philosophy faces (one that in turn reflects the significance of the political issues that are at stake). My own view, and thus my attempt at meeting this challenge, acknowledges the existence of multiple grounds of justice. This book seeks to present a foundational theory that makes it plausible that there could be multiple grounds of justice and to defend a specific view of the grounds that I call pluralist internationalism. Pluralist Internationalism grants particular normative relevance to the state but qualifies this relevance by embedding the state into other grounds that are associated with their own principles of justice and that thus impose additional obligations on those who share membership in a state. The grounds that I discuss are shared membership in a state; common humanity; shared membership in the global order; shared involvement with the global trading system; and humanity’s collective ownership of the earth. (It is probably in the conceptualization of common ownership as a ground of justice that my view seems strangest.) Within this theory one must explore what obligations of justice pertain to states and other institutions. International institutions must be understood as agents of justice (rather than as entities that merely advance particular state interests). Moreover, it is international organizations or other entities of global administrative law that most plausibly create the context in which states give account to noncitizens for their contributions to justice.