This book, authored by International Court of Justice Judge Yuji Iwasawa, builds on decades of reflection on the topic of direct applicability of international norms within a domestic legal system. As the author explains in the preface, the issue sparked his interest as a young academic in relation to domestic courts’ application of international human rights treaties. As he began researching it in more depth, he noticed that “the doctrine of self-executing treaties was in a state of confusion and in great need of clarification and reformation.”Footnote ¹ While most of the research was conducted several decades ago (which explains why some of the references are dated), the book strives to include recent developments, and some parts have been substantially revised or developed, especially in Chapters 2 and 5.Footnote ²

As the title and subtitle of the book make clear, direct applicability is but one dimension of the domestic application of international law. Judge Iwasawa reminds his readers that “the question of the domestic status of international law involves three separate issues: force of law, direct applicability, and rank.”Footnote ³ While the distinction between force of law (or validity), direct applicability, and rank will seem obvious to the readers of this review, these aspects are sometimes confused in practice (see, for example, in the US context).Footnote ⁴

The book is divided into seven chapters. After a short introductory chapter, Judge Iwasawa presents the “international approach” to direct applicability in the second chapter. The third chapter focuses on the US doctrine of self-executing treaties, while the fourth chapter deals with the direct effect of European Union (EU) law. As the author explains,Footnote ⁵ this structure was chosen because the doctrine of direct applicability has three main “sources”: the case law of US courts, the advisory opinion of the Permanent Court of International Justice (PCIJ) in Jurisdiction of the Courts of Danzig, and EU law.Footnote ⁶ Approximately half of the book is devoted to these three “sources.”

The fifth chapter, by far the longest of the book (more than eighty pages), presents “a framework of analysis” for the domestic application of international law. By contrast, the sixth chapter is among the shortest (thirteen pages) and focuses on customary international law (CIL) and acts of international organizations. The seventh and last chapter deals with judgments of international courts. A short conclusion wraps up the book. This review focuses on four aspects of the book that warrant further discussion. First, what are the interpretative issues raised by direct applicability? Second, is direct applicability a question of international law, domestic law, or both? Third, the review examines the implications of the author’s main claims for international legal practice and scholarship. Finally, it discusses some of the author’s methodological choices, especially in terms of case selection.

One issue that deserves further analysis pertains to the interpretative issues raised by direct applicability. As the author makes clear from the beginning of his analysis, the issue of direct applicability raises a number of interpretative questions. The study can be read as an attempt to clarify the interpretative methodology that should be applied to determine whether an international legal norm is directly applicable. The author explains that the mere fact that an international legal norm needs to be interpreted in order to be applied does not mean that it is not directly applicableFootnote ⁷ – though it seems difficult to argue otherwise, given the pervasiveness of interpretation in international law (and law in general). Judge Iwasawa rightly highlights that, like many other interpretative questions, the question of direct applicability arises not only with regard to written norms but also with regard to unwritten ones (CIL).Footnote ⁸

An important reference point for the doctrine of direct applicability in international law is the aforementioned advisory opinion of the PCIJ, which is based on the idea that the criterion to determine direct applicability is the intention of the parties.Footnote ⁹ Judge Iwasawa disagrees with this view, highlighting the flaws of what he calls the “international” (and, one might add, “intentional” or “voluntarist”) approach.Footnote ¹⁰ Throughout the book, he insists that the intention of the parties, because it cannot be identified with certainty, is “fictitious.”Footnote ¹¹ Because it is unreliable, the parties’ intent “should not be used as a criterion to determine the direct applicability of international law.”Footnote ¹² One could add that intentionalism is a normative interpretative theoryFootnote ¹³ (which one may or may not endorse) but not an accepted interpretative method of international law, even if the methods prescribed by Articles 31–33 of the Vienna Convention on the Law of Treaties (VCLT) (and, especially, the historical and teleological method) may involve an inquiry into the will of the parties.Footnote ¹⁴ It is worth noting that the author rarely refers to these interpretative methods, except for his frequent reliance on the travaux préparatoires, which, according to Article 32 of the VCLT, are only “supplementary means of interpretation.”

Distancing himself from the Danzig opinion, Judge Iwasawa proposes what he calls a “relative approach” to direct applicability. In his view, “[w]hether or not international law is directly applicable must … be determined depending on the context in which it is invoked and applied.”Footnote ¹⁵ In other words, the assessment of direct applicability needs to be case specific. There is no doubt that a context-sensitive appraisal of direct applicability has some advantages, such as flexibility and pragmatism: law is an interpretative practice that materializes when general and abstract norms are applied to individual and concrete cases. Thus, by definition, legal interpretation (the attribution of meaning to a legal norm) requires doing justice to the specificities of a given case. At the same time, the relative approach also has important drawbacks, not least that it risks being guided by the interpretative result. This is precisely one of the methodological problems that can be witnessed in relation to direct applicability – for instance, in the interpretative practice of domestic courts.Footnote ¹⁶ One could therefore argue that one of the main disadvantages of the relative approach is its unprincipled nature. This, in turn, seems to stand in tension with Judge Iwasawa’s goal of bringing more analytical clarity to the assessment of direct applicability. We will come back to this aspect when discussing the implications of his analysis.

A second question that pervades the book is the following: is direct applicability a question of international law, domestic law, or both? This question is directly related to the first issue and, therefore, to the Danzig advisory opinion. As Judge Iwasawa explains, “those who rely on this Opinion as the authority on the concept of direct applicability tend to believe that whether international law is directly applicable is a question of international law because it concerns the interpretation of the intention of the parties.”Footnote ¹⁷ This view, which is held by “[m]any scholars in Europe,”Footnote ¹⁸ has also been called the “pre-existence theory” or the “given theory” because it deems direct applicability to be “a pre-existing attribute of international law.”Footnote ¹⁹ Again, the author decidedly disagrees with the approach of the PCIJ, according to which direct applicability is a question of international law: “While these views are held by many scholars and courts, they are questionable.”Footnote ²⁰ For him, direct applicability is a question of domestic law. It depends, among other things, on the existence of domestic structures of implementation, for example, in connection with the European Convention on Human Rights. Footnote ²¹ This claim is not unproblematic, as it seems to play in the favour of states in which such structures are lacking. However, it is important to read Judge Iwasawa’s analysis carefully; the author himself wants to make sure that his argument (namely, that direct applicability is a question of domestic law) is not misunderstood. As he explains, “[i]t does not follow from this position that only domestic factors need to be considered, much less that the intention of one’s own State is controlling,” even if in some states (such as the United States), courts and scholars argue otherwise.Footnote ²²

But then (and this brings us to the next dimension of the book), what are the implications of this analysis for international legal scholarship and practice? First, in several important respects, Judge Iwasawa’s meticulous study contributes to more analytical rigour and conceptual clarity in the assessment of direct applicability (something that is also needed when it comes to the domestic application of international law in general).Footnote ²³ The author shows that direct applicability is often confused with issues that are conceptually distinct, including validity — for example, with respect to the United States,Footnote ²⁴ the creation of individual rights,Footnote ²⁵ or standing.Footnote ²⁶ Throughout his analysis, he challenges many of the criteria used by international, supranational, and domestic institutions as well as legal scholars to determine direct applicability (see especially Chapters 2–4) and highlights that numerous different conceptions of direct applicability coexist.Footnote ²⁷ He also calls for greater semantic precision. For instance, he compellingly shows that the term “self-executing” should be avoided because it is “bound to give rise to confusion.”Footnote ²⁸

Second, by pinpointing the lack of a homogeneous approach with regard to direct applicability, Judge Iwasawa seems to implicitly call for greater consistency.Footnote ²⁹ However, the question is whether such consistency is compatible with the relative approach and with the position that direct applicability is a domestic legal issue – unless one insists that the relative approach consists in a case-specific assessment, to the exclusion of criteria that are actually irrelevant when determining direct applicability. The author’s call for consistency sometimes becomes more explicit — for example, when he examines direct applicability in international law and EU law. For him, “the concept of direct applicability is not fundamentally different in international law and EU law’; rather, he deems this concept “valid for any law, regardless of whether the law is international, European, or national.”Footnote ³⁰ The author goes so far as to say that to argue otherwise would be equivalent to “overstat[ing] the uniqueness of EU law or hav[ing] an inaccurate understanding of international law.”Footnote ³¹

Third, Judge Iwasawa is hopeful that “[o]verall, the relative approach will significantly enhance the effectiveness of international law in domestic law.”Footnote ³² Yet there are two possible readings of the relative approach. On the one hand, it may be völkerrechtsfreundlich not only because it may encourage greater consistency but also because the author argues for a presumption of direct applicability — that is, for a broad interpretation of the concept.Footnote ³³ On the other hand, the relative approach seems to leave significant leeway to states, especially in light of Judge Iwasawa’s claim that direct applicability is something for domestic law to determine. Under this reading, direct applicability leaves almost unlimited discretion to states. In this respect, the sword and the shield metaphor,Footnote ³⁴ which is used by several scholars in relation to direct applicability, is telling.Footnote ³⁵ It illustrates the instrumental nature of the concept, which may be used either to undergird (that is, as a sword) or, to the contrary, to undermine (that is, as a shield) the domestic application of international law. Direct applicability thus becomes a means towards certain ends.

At the very end of the book, Judge Iwasawa acknowledges that “[t]he doctrine [of direct applicability] can thus give additional pretexts to domestic institutions to refuse the application of international law in domestic law.”Footnote ³⁶ That this remark appears so late in the analysis is surprising, as states’ instrumental use of direct applicability is precisely one of the main challenges that arises in relation to the relative and “domestic law” approach. In light of this challenge, it is unclear whether the book will truly “facilitate the domestic application of international law.”Footnote ³⁷

This brings us to what is perhaps one of the least explored areas of the book. The analysis primarily focuses on conceptual and technical aspects, while placing little emphasis on the broader ramifications of direct applicability and on other aspects that would be of interest to the reader, such as: why does this question matter and what are the areas of international law (and the domestic interests) most concerned by the question of direct applicability? The author could be more candid about what is at stake in connection with direct applicability and more transparent about the implications of his theory. In particular, what are the implications of claiming, as he doesFootnote ³⁸ and as US courts and scholars also do,Footnote ³⁹ that direct applicability is a matter for domestic legal orders to settle? Why not accept that the direct applicability of international legal norms is an interpretative question that, as such, is governed by the interpretative methods of international law — namely, by Articles 31–33 of the VCLT?

Finally, a few words about the author’s methodological choices. First, the study gives significant weight to the practice of the United States,Footnote ⁴⁰ even if this practice is not necessarily viewed as convincing in every aspect. As the author notes, “many domestic cases addressed in this book are from the United States.”Footnote ⁴¹ The importance given to the United States is certainly justified in some respects. For instance, the author’s account of the history of the doctrine of self-executing treaties is highly informative.Footnote ⁴² On the other hand, one may wonder whether the United States ought to be given so much importance in a study devoted to direct applicability, especially given its ambivalence towards international law, its tendency towards unilateralism, and its propensity to prioritize its own interests. For instance, Curtis Bradley’s view that only the intent of the US treaty makers (and not that of the treaty parties as a group) is relevant is difficult to square with the interpretative methods of international law.Footnote ⁴³ Judge Iwasawa himself disagrees with this view, stating that it is the intent of all treaty parties that matters.Footnote ⁴⁴ More generally, it seems problematic to rely on the practice of a handful of powerful states (including the United States) in relation to direct applicability.

Second, the author also refers to the practice of other states, though these other cases “are discussed only when they are relevant to the issues addressed.”Footnote ⁴⁵ As he highlights, “[d]ue to the limited accessibility of certain materials, the other examples … come mostly from European States.”Footnote ⁴⁶ While the author mentions many domestic examples, he does not tell us much about their context and comparability. When can one rely on this case law? Are there “families” of jurisdictions warranting internal cross-fertilization? Moreover, the issue of accessibility mentioned by the author shows that, de facto, the practice of some states has more weight than others in international legal research.

Third, while it seems essential to include CIL, as Judge Iwasawa does in Chapter 6,Footnote ⁴⁷ the section devoted to this source of international law is very short (only five pages). This leaves the reader wondering why it was not examined in more depth and whether it would not have been better to leave it out entirely. Similarly, given their status as a source of international law, one may ask whether it would not have been appropriate to devote a section to general principles of international law, instead of discussing acts of international organizations (Chapter 6)Footnote ⁴⁸ and international judgments (Chapter 7).

To conclude, the author has completed a highly impressive and detailed study of the concept of direct applicability, which calls for greater rigour in the way in which this concept has been approached in legal practice and scholarship. Despite serving on the ICJ, Judge Iwasawa disagrees with the ICJ’s predecessor, the PCIJ, on several counts, especially with its approach focused on the notion of intention of the parties and its treatment of direct applicability as an international legal issue. Direct applicability is an important area of friction between public international law and domestic law due to the propensity of states to use it as a tool to further specific ends. Hence, the author’s call for greater methodological rigour is welcome, and his study a must-read for anyone studying direct applicability. Still, one may wonder whether this analysis (especially the relative approach and the argument that direct applicability is a question of domestic law) does not bear the risk of encouraging self-serving interpretations by states that are reluctant to apply international legal norms. Whether intended or not, this implication may seem at odds with what Judge Iwasawa calls the presumption of direct applicability and, more fundamentally, with the objective of contributing to a more effective domestic application of international law.