Anarchy is the conceptual cornerstone of international relations theory and international law scholarship. Anarchy is described as the ordering principle of the international system, it is used as a variable that explains state behaviour, and the international legal order is depicted as anarchic and decentralised. This article questions this privileged status of anarchy. It challenges the designation of anarchy as the ‘ordering principle’ of the international system, and proposes an alternative theoretical construct – the Constitutive Regime of the International System – that performs the functions of the ‘ordering principles’ of the international system. This Constitutive Regime consists of three components. The first is a principle of differentiation that identifies the constituent units of the international system. The second is a theory of world order that prescribes policies and principles that are necessary to maintain order within the system, and the third are the secondary rules of international law that generate the international law-making and law-enforcement processes. In short, the Constitutive Regime provides a novel theoretical vernacular to understand and conceptualise the normative foundations of the international system.

This review explores certain challenges related to the notion of customary international law. It seems that it was a long time ago when international law academics and practitioners ever thought that the nature of this source was a well-settled topic. Nowadays international lawmaking processes involve an extraordinary number of interactions, taking place both formally and informally. Such complex features are reflected by an exponential increase in the scholarly study of international legal sources. The legal nature, its applicability and principles regulating customary international law are addressed in the book under review (Brian D Lepard (ed), Reexamining Customary International Law (Cambridge University Press 2017)) through several topical essays. The chapters offer a comprehensive analysis of these lawmaking processes and the challenges they portray from various perspectives and in various fields, such as: What is customary international law and why is it law? Is it law because it reflects a ‘global legislative’ model? What is the current value of the persistent objector theory? Is the two-element definition of customary international law still applicable? By meticulously addressing these and other inquiries, the book presents novel arguments and represents a stimulating addition to the literature on sources of international law.

This review of Non-State Actors in International Law, edited by Math Noortmann, August Reinisch and Cedric Ryngaert (Hart Publishing, 2015), focuses on the constraints of state-centric approaches in accurately depicting the role and status of non-state actors in the international arena. As the book presents a comprehensive examination of the influence of diverse entities in a variety of fields, such limitations are evidenced and inevitably lead to the reassessment of novel theoretical standpoints, as well as to the recognition that a multidisciplinary approach is much needed in order to advance further studies on the issue.