This book has been a long time in the making. While the actual writing started in 2009 and took place, intermittently, until May 2012, the book reflects more than twenty years of teaching international law. The basic premise underlying it is that international law should not be studied as a vast and ever-increasing collection of rules, but is better approached as a way of thinking about and organizing the world. With that in mind, like all legal systems the international legal order can profitably be studied by asking four questions. First, there is the question of where the law comes from: what are its sources? Second, to what entities or individuals does the law apply or, in other words, what are its subjects? Third, what does the law do in cases of conflict (i.e. settlement), and finally, what does the law actually say? What is its substance?

This book is organized with those four questions in mind. The first three, together pointing to the basic structure of the system, make up Part I of this book (Chapters 1–9): sources, subjects and settlement, broadly conceived. This is the stuff all international lawyers (probably even all lawyers, in these days of globalization) will sooner or later be confronted with; all lawyers need to have some idea of how international law is made, in what circumstances states can be held responsible, how international tribunals function and whether or not specific entities are subject to international law.