This book contributes to our understanding of one of the most pressing issues of modern international law: the relationship between the international legal order and the domestic legal orders of over 190 sovereign states.The traditional and dominant understanding of this relationship is that there exists a strict separation between the international legal order and domestic legal orders. Processes of legal globalization and internationalization have made this relationship much more complex. Legal authority has shifted away from the state in both vertical and horizontal directions. Forced by the pressures of interdependence, states have allowed international bodies to oversee and sometimes even implement and enforce domestic legislation. At the same time, private persons are more and more drawn into an internationalized order. Increasing cross-border flows of services, goods and capital, mobility, and communication have further undermined any stable notion of what is national and what is international. This book offers several partly complementary and partly competing perspectives that allow us understand and make sense of the complex interaction between the international and domestic sphere.