This text is a comprehensive study of differential treatment for developing countries in international environmental law. It offers an analysis of the legal dimension of the relationship between developed and developing countries in the environmental field and beyond. It first critically examines the principle of legal equality of states and then explores the conceptual framework behind the notion of differential treatment in international law and its relevance in bringing about substantive equality. The book examines the development of differentiation in international environmental law, considers its application in various environmental treaties and evaluates the legal status of existing differential norms. It also examines the contribution of differentiation to the implementation of environmental treaties and the extent to which differential treatment fosters the decentralization of international environmental policy making. It is a useful resource for all actors involved in environmental law and policy making, scholars and students.