Transnational Social Justice engages with the current debate on cosmopolitanism by presenting a new way to justify obligations of distributive justice between countries. This book offers an overview of the mainstream cosmopolitan theories that have attempted to philosophically defend the validity of global justice. It presents a theoretical approach, grounded in the tradition of international ethics, which seeks to overcome the major challenges put forward by critics of transnational arrangements of distributive justice. Drawing on Hedley Bull's idea of the international society, this work develops a fresh model of the contemporary system of states characterized interdependence, which allows the introduction of a distinctive international normative framework. The book argues that the existing ethical structure of the system of states, grounded on solidarity rather than autonomy, has paved the way for specific conditions of social justice across nations, which seek to overcome outmoded notions of aid.