International law scholarship today is variable. As in other areas of legal scholarship, there have been debates between formalists and realists. International law scholarship grounded in other approaches, such as naturalism, pragmatism, institutionalism, and transnational legal process, has also engendered sophisticated scholarly debates both within and between these techniques. According to two leading commentators, there may be as many as seven dominant methods of international law scholarship: “legal positivism, the New Haven School, international legal process, critical legal studies, international law and international relations, feminist jurisprudence, and law and economics.”Footnote ¹ This wealth of perspectives is due in part to the fact that political and economic realities impact local conditions differently. When writers reflect on international law, they bring the commitments of the legal and political cultures from which they write, at least in part, to the conversation, thus contributing to the pluralism of international law scholarship.

Most in vogue at present is an “empirical turn” in international law scholarship.Footnote ² Empiricism has been ascendant because many believe that “[i]nternational legal scholarship has long suffered from too much normative theorizing and too little positive analysis about how the international legal system actually works.”Footnote ³ As such,

Importantly, while this

Even with the ascendance of empiricism, international law scholarship today frequently does not employ one single method; it often combines methodological approaches, and has thus engendered many mixed methods. The turn to empiricism has challenged but not replaced other international law methods.Footnote ⁶

As important as method is, theory is also a key part of international law. This is so because “[u]nlike other legal disciplines, international law usually involves a commitment on the part of those who have recourse to it.”Footnote ⁷ The question is how to explore international law and its approaches fully, with a firm grasp of the long tail of history and of the varied approaches in a way that engages the reader to reflect on her commitments at the time of writing (and reading). Taking account of international law's doctrinal, methodological, and theoretical mélange is a very tall order.

A welcome example of a cross-disciplinary approach that accepts the challenge and returns international law to its theoretical roots is The Oxford Handbook of The Theory of International Law, edited by Anne Orford, Redmond Barry Distinguished Professor, Michael D. Kirby Chair of International Law, and Kathleen Fitzpatrick Australian Laureate Fellow at Melbourne Law School, and Florian Hoffman, Professor of Law and Director of the Willy Brandt School of Public Policy at the University of Erfurt, with the assistance of Martin Clark, Research Fellow and Tutor at the Melbourne Law School. This timely and important handbook consists of an Introduction and forty-eight original essays that are authored by a veritable “who's who” of international scholars.

The authors and editors seek

In so framing the Handbook’s goals, the editors have the good sense not to seek to impose any coherence to the field of international legal theory. Rather, they hope to convey “a sense of the theory of international law as a wide-ranging tradition that is dynamic, pluralist, and politically engaged” (p. 17).

The Handbook is organized in four parts. Part I, which consists of thirteen chapters, falls under the heading of “Histories.” The first several chapters by Matthew Craven, Randall Lesaffer, and Martti Koskenniemi, explore the turn to history in international legal theory. In the words of Craven, “why this sudden interest” in the history of international law “at the expense of other forms of analytical or critical endeavors?” (p. 21). Koskenniemi's partial answer is that “[a]n examination of whether jurists have been more inclined to engage in the routines of legal work or debates about the frame tells us much about the law's relationship with the surrounding world” (p. 59). Between these two chapters, Lesaffer offers a very readable examination on the ways in which Roman law influenced and continues to influence the development of international law.

Contributions by Martine Julia van Ittersum, Emmanuelle Tourme-Jouannet, Umut Özsu, Teemu Ruskola, Jochen von Bernstorff, Robert Howse, Deborah Whitehall, and Lauri Mälksoo explore theory and history by grounding their discussions in the people (Grotius, Vattel, Kelsen, Arendt) and places (Europe, the Ottoman Empire, China, Russia) where different theoretical interventions have arisen. In these chapters, significant attention is paid to the fact that different historical circumstances inform theorizing about international law, and thus that international law theory is not linear.

Part II takes the reader from history to “Approaches.” These thirteen chapters undertake “a recurrent engagement with the traditional mode of classification, notably by reference to a limited set of master narratives or ‘schools of thought’ deemed to have shaped the theory landscape” (p. 11). The contributors, while “not purport[ing] to offer an encyclopaedic overview of all the different modes in which international legal theory is undertaken today” (p. 11), comprehensively examine natural law (Geoff Gordon), Marxist approaches (Robert Knox), realism (Oliver Jüttersonke), constructivism (Filipe Dos Reis and Oliver Kessler), international signs law (Peter Goodrich), moral philosophy (Samantha Besson), positivism (Jörg Kammerhofer), Yale's policy science, (Hengameh Saberi), law and economics (Dan Danielsen), liberal internationalism (Daniel Joyce), feminist approaches (Dianne Otto), cosmopolitanism (Wouter Werner and Geoff Gordon), and global administrative law (Benedict Kingsbury, Megan Donaldson, and Rodrigo Vallejo). While wide-ranging, this part would have benefitted from a stand-alone essay on global legal pluralism.

Part III, consisting of seventeen chapters, explores “Regimes and Doctrines.” The contributions in this part look at “the role of theory in relation to canonical subjects of general international law …” (p. 12). Chapters by Jean d'Aspremont, Gerry Simpson, Rose Parfitt, Gregor Noll, Jan Klabbers, Fleur Johns, Dino Kritsiotis, Ben Golder, Anne Orford, Sarah Nouwen, Frédéric Mégret, Vasuki Nesiah, Stephen Humphreys and Yorko Otomo, Kerry Rittich, Outi Korhonen and Toni Selkälä, Horaita Muir Watt, and Chantal Thomas ably take the reader through subjects such as sources, statehood, state responsibility, jurisdiction, international criminal law, international human rights law, international trade law, private international law, and globalization. Given recent events, such as Brexit and Syria, Thomas's chapter on “Transnational Migration, Globalization, and Governance: Theorizing a Crisis” is particularly timely.

Finally, Part IV consists of five chapters and is dedicated to “Debates” surrounding international legal theory. The contributions in this part are both descriptive and critical, and seek to reveal to the reader the essential and contested nature of international legal theory's “current state and likely future” (p. 14). Reut Yael Paz addresses religion, secularism, and international law. Thomas Skouteris writes about the idea of progress. Florian Hoffman's contribution is concerned with international legalism and international politics. Jason Beckett writes on international law and its relation to poverty. Finally, Anne Peters's chapter discusses fragmentation and constitutionalization.

While each part of the Handbook is not internally organized to ask or answer any one question, each part does leave the reader with important takeaways. In Part I, one gains a special appreciation for the historicity of legal theory, and one begins to value even more the caution that should be exercised when transplanting a given theory outside of its original time and place. Part II's concern with approaches drives home the point that lawyers love systems of classification. These systems create their own internal systems of critique and contestation that lead to other systems that then compete for ascendance. Part III's exploration of regimes and doctrines reaffirms that social transformation is a key catalyst for theory. Finally, Part IV's detailing of debates offers a welcome way to conceptualize all that has come before in the previous parts.

The breadth, depth, and sophistication of this Handbook is remarkable, and the editors and authors deserve thanks and praise. Indeed, it is particularly noteworthy that the Handbook focuses on international law in both its public and private dimensions. With that said, the Handbook would be even more pioneering had it dealt directly with the relationship of public international law to private international law from a theoretical perspective. Arguably, Muir Watt's chapter on theorizing private international law attempts this, but additional consideration of the subject would have been a welcome and important addition to the Handbook’s stated goals.

There is, however, at least one glaring omission in the Handbook’s coverage: The absence of any extended consideration of international investment law and international arbitration generally is a significant missed opportunity. Indeed, if there is any contemporary area of international law that is ripe for theoretical investigation, it is this one. For example, the following puzzles call for sustained inquiry: Is international investment law public or private law? Is it appropriately analogized to international arbitration, or does the fact that investor-state arbitration involves a treaty counsel in favor of considerations of transnational public governance?Footnote ⁸ Besides contract terms and applicable law, is there a customary international law of arbitration that tribunals and counsel may turn to? If so, what are its contents? Last but not least, what does the empirical turn in international arbitration scholarship mean for the discipline. Of course, keeping with the Handbook’s organization, these and other arbitration-related subjects could also be viewed through the history, approaches, doctrines, and debates lenses. This Handbook provides a useful framework and starting point to begin to answer these questions.