1. Introduction: differentiation theory and international relations Mathias Albert, Barry Buzan and Michael Zürn; Part I. Sociological Perspectives: 2. Rationalized cultural contexts of functional differentiation George M. Thomas; 3. The history and systematics of functional differentiation in sociology Rudolf Stichweh; 4. Functional, segmentary, and stratificatory differentiation of world society Richard Münch; Part II. On the Differentiated Structure of the International System: 5. Differentiation: type and dimension approaches Jack Donnelly; 6. Stratificatory differentiation as a constitutive principle of the international system Lora Anne Viola; 7. Some quanta of solace: world politics in the era of functional differentiation Stephan Stetter; Part III. On the Interplay of (Global) Function Systems: 8. Functional differentiation and the oughts and musts of international law Oliver Kessler and Friedrich Kratochwil; 9. International institutions in a functionally differentiated world society Mathias Koenig-Archibugi; 10. Functional differentiation, globalization and the new transnational neo-pluralism Philip G. Cerny; 11. Conclusion: differentiation theory and world politics Michael Zürn, Barry Buzan and Mathias Albert.