'Great news: world society exists! In his fascinating new book, Mathias Albert tells the story of the evolutionary emergence and organization of world politics, situating it in a sophisticated theoretical framework for which social differentiation is the key to understanding the evolution of society in general and, thus, also the key to understanding world society (Part 1) and world politics (Part 2). Even though Albert is professor of political science (at the University of Bielefeld), A Theory of World Politics is mainly written for an international relations audience and is informed by sociology and history, this book is a valuable read for international legal scholars as well. If you are prepared to face some theoretical challenges, you can learn a lot about how world politics emerged and how it is organized today, which is arguably an important field for international lawyers in an insecure 'Trump era'.' Lando Kirchmair, European Journal of International Law