This chapter outlines the rationale of the book. The core objective is to provide some clarity to what is meant by phrases such as ‘international society at the global level’ or ‘global international society’ (GIS). Our starting assumption is that the answer to this question is far from clear. And without being able to specify the composition and characteristics of GIS in some concrete way, it is not really possible to answer questions either about how GIS was and is composed, and whether it was and is getting stronger or weaker. The chapter situates these questions in broader International Relations and social science debates, outlines our approach to the questions and discusses how this approach builds on our previous research. It then discusses the aims of the book in detail and closes with a summary of the book’s contents.