Hedley Bull’s theory of international relations has widely been treated as of central importance within the international relations discipline. Yet, Bull’s theory is inherently interdisciplinary, not least because the basic elements it operates with, such as “international society” and “international order”, inevitably draw on the factors and considerations that constitute the legitimate object of the discipline of international law. Thus, the proper understanding and evaluation of the genuine importance of Bull’s theory requires an interdisciplinary analysis that is being undertaken here for the first time, in order to understand the genuine essence of his theory as well as the implications of it for the practical aspects of both law and politics in international affairs.