Deference, standard of review and margin of appreciation are key concepts to understand how international tribunals adjudicate matters involving States' measures and actions. When an international tribunal shows ‘deference’ towards a decision adopted by a State, it acknowledges both the primacy of the State to make such a decision and the need to avoid substituting the State's judgement with its own. For their part, ‘standard of review’ and ‘margin of appreciation’ are the concepts employed when examining the degree of deference granted by international courts to States' actions. Although these two terms are sometimes used indistinctively to refer to the same thing (i.e. the level of intrusiveness used by a court or tribunal when assessing a State's measure), strictly speaking, the ‘standard of review’ concept does not mandate any specific level of deference, whereas the ‘margin of appreciation’ notion – more used in the field of human rights law – incorporates or recognizes the existence of some deference.

Standard of review and margin of appreciation are tools used by international courts to determine the degree of deference that must be granted to States' actions when such actions are examined in the light of States' international obligations. However, unlike national legislation, the applicable standards of review are almost never explicitly articulated in international treaties (with some notable exceptions such as Article 17.6 of the WTO Anti-Dumping Agreement). As a consequence, it is for each tribunal to determine whether deference to national authorities' determinations should be warranted and to what extent; or if, on the contrary, judges may undertake a de novo review, substituting their own assessment for that of the State concerned, and arrive at a different conclusion (p. 319). In the absence of explicit provisions in international legal instruments that deal with the applicable standard of review, publications like this one become especially useful, since they compile and systematize the practice and jurisprudence of different international adjudicative bodies. Indeed, this excellent book provides insightful perspectives on how different international courts proceed to exercise their adjudicating power using standard of review and/or margin of appreciation as instruments for either judicial self-restraint or judicial activism.

The book is divided in five parts, each containing several chapters authored by different contributors. Part I covers general, theoretical issues, such as the principles of justice, democracy, and good faith, as well as their relevance in evaluating different standards of review. It contains four chapters that take a comparative approach and examine the practices of different international tribunals. Chapter 3, for instance, describes different methodological approaches taken by European Union (EU) courts, World Trade Organization (WTO) dispute settlement bodies, and investment tribunals when dealing with public policy exceptions, each of them providing a different level of deference. Notably, there appears to be ‘significant convergence of practice’ in reviewing measures justified as public policy. However, deference appears most restricted in the case of the EU and more liberal in the WTO context (probably due to the disparity of membership and limited objectives of the WTO compared to the EU), with significant variation in the case of arbitral tribunals (p. 56).

Part II also contains four chapters and deals with the applicable standards of review in WTO law and international investment law. Chapter 6 concentrates on the applicable standard of review in the WTO context and notes that the debate around that topic is still dominated by ‘obscure and indeterminate notions’ such as ‘objectiveness’ and ‘reasonableness’. It suggests, instead, a participation-reinforcing criterion, according to which greater deference is awarded to decisions resulting from an inclusive and sufficiently open procedure (pp. 111–112). Chapters 7 and 8 take the discussion into the field of international investment law. In the authors' view, investment tribunal decisions adopt a wide range of approaches when determining the legality of the exercise of public power by States, but such decisions do not clearly set out the rationale for the approach employed in every instance (p. 133). Although some tribunals have applied a strict standard of review, the contributors clearly advocate for greater deference towards host States, especially in situations of normative or empirical uncertainty. The last chapter of Part II compares the approaches adopted in WTO law and international investment arbitration when reviewing national regulatory measures based on scientific determinations. It observes that, despite some divergences, WTO adjudicative bodies and investment arbitration tribunals converge in rejecting an intrusive de novo review and in adopting a deferential approach when confronted with domestic decisions based on scientific determinations made at the municipal level (p. 171).

Part III is devoted to EU law. It contains three chapters that deal mainly with the standards of review applied by the Court of Justice of the EU (CJEU). While Chapter 10 seeks to distinguish different standards relied upon by the CJEU – reflecting varying degrees of intensity in the review of national procedural choices depending on whether such choices frustrate or foster the European integration process – Chapter 11 analyzes the applicable standard of review in risk regulation cases – confirming that there has been a certain evolution of the CJEU's standard of review, which has moved from a deferential to a more restrictive one (pp. 190 and 208). In addition, Chapter 12 compares the standards of review used by the CJEU and the WTO dispute settlement bodies in ‘necessity’ and ‘proportionality’ analyses. The authors argue that judicial deference is appropriate in cases involving factual or normative uncertainty, but that courts should grant deference on substance only after actively reviewing the procedural fairness on the way the domestic decision was reached (p. 231).

Part IV of the book concentrates on international human rights law. The first three contributions review various aspects of the margin of appreciation doctrine in the case law of the European Court of Human Rights (ECtHR). Chapter 13 looks at the concept of margin of appreciation through the lens of standard of proof because both concepts are, according to the author, closely connected (pp. 251–252). Chapter 14 reviews the recent hate speech cases before the ECtHR, noting that the Court lacks a consistent approach and seems unwilling to explain its rules for privileging certain opinions over others (p. 271). Chapter 15 examines the concept of ‘standard of equivalent protection’, which is used in European human rights law and encompasses the notion that measures adopted under the EU system do not need to be reviewed as long as such a system ensures human rights protection equivalent to that of the European Convention on Human Rights (p. 272). For its part, Chapter 16 focuses on the Inter-American context and explains the reasons behind the Inter-American institutions being quite hesitant to show deference to national agencies when assessing cases of human rights violations (p. 314).

Finally, Part V of the book takes a look into other international courts such as the International Court of Justice (ICJ), the International Tribunal for the Law of the Sea (ITLOS), and the International Criminal Court (ICC). Chapter 17 analyzes the jurisprudence of the ICJ and notes that the Court shows different levels of deference depending on the nature, aim, and characteristics of the norm involved, being more restrictive, for instance, when fundamental concerns are at stake (p. 336). Chapter 18 stresses that the concept of standard of review has received little attention in the field of the law of the sea, and thus examines this notion in the context of the ITLOS' prompt release jurisprudence. The author questions whether the Tribunal has achieved the required balance between coastal and flag States interests (p. 353). The last two contributions focus on the practice of the ICC. In that regard, while Chapter 19 analyses the approach of the Court in admissibility proceedings initiated by States, Chapter 20 examines the relationship between the concept of standard of review and the principle of ‘complementarity’, according to which States have priority in the prosecution and punishment of mass atrocities and the ICC may only intervene if States do not genuinely combat impunity (p. 371).

This book, therefore, has a comprehensive scope and, to a great extent, offers a good overview of the varying jurisprudence regarding the degree of scrutiny applied by international courts when reviewing States' actions. Precisely because it covers a wide range of tribunals and their case law, the book does not go into great detail when examining each of them. Moreover, at least in the WTO-relevant section, the contributions contain many interesting remarks on how standard of review should be approached by panels and the Appellate Body and what criteria they should use to award deference to Member States' trade measures; less time is spent on simply describing the standard of review that actually is applied by the WTO judicial bodies across the different WTO Agreements. Nonetheless, this should not be taken as a criticism for a contribution that does not intend to be a handbook, but rather a collection of essays on the topic of deference that gathers different views and perspectives from experts in various fields of international law.

Despite being a compilation of independent contributions, however, some overall conclusions can be extracted from the book, as observed by the editors in their introduction. A reading of all 20 chapters confirms that the role of each court must be examined in the light of the broader political and historical context in which they operate. Moreover, even within the same court, it is not uncommon to see diverging positions towards the question of judicial review. Interestingly, however, notwithstanding the differences that exist, international tribunals eventually face the same problems and deal with them in similar ways, using overlapping criteria to determine the intensity of judicial review and the degree of deference to be granted to States' measures.

In conclusion, the book does an excellent job in showing the diversity of approaches adopted by different international courts, but it does not purport to provide detailed information on every aspect related to standard of review in international law. Therefore, practitioners, and other interested readers, should not view this contribution as a guidebook or manual on the use of deference by supranational adjudicative bodies. Instead, they should see it as an enriching collection of essays that contains an interesting variety of viewpoints and allows the reader to obtain a genuine comparative perspective on how the principles of standard of review and margin of appreciation are applied by international courts and tribunals.