This book considers the ways in which a cosmopolitan vision might constitute the ethical basis for the validity criteria of a new world order, and thus the basis for the validity of international law in a future global political reality. It examines the transformation of some of the fundamental pairs of concepts associated with the change of the concept of the state in our post-national epoch, and it analyzes the change of the perception of the legal subject and the new role of the individual person in international law after the Second World War.