In 1997, "The Society of Society," the main work of social theory by Niklas Luhmann, was published. The system-theoretical perspective developed within it, encapsulated in the fundamental formula that society cannot be thought of without communication and communication cannot exist without society, has since provided crucial impulses not only for sociology. The various aspects of communication, evolution, differentiation, and observation that Luhmann derives from his investigation, as well as his idea of world society, are the subjects of this collection of materials. The authors critically engage Luhmann's social theory with other sociological perspectives, thereby attesting to the relevance and power of this classic of modern sociology.