Through her work at the World Trade Organization (WTO) Secretariat<fnref n="1" /> and scholarship, Gabrielle has contributed to better understanding the WTO covered agreements and their importance, including through their interpretation, as a source of public international law. Whilst Gabrielle’s academic writings cover many other topics, a common thread has been her interest in mainstreaming WTO law as part of public international law.

I first learnt about Gabrielle’s scholarship on treaty interpretation while working on my doctoral thesis on the same topic. I remember meeting with Gabrielle after she had kindly offered to read a few draft chapters of that thesis and was keen to learn more about the work of the International Law Commission (ILC) Study Group on “Fragmentation of international law: difficulties arising from the diversification and expansion of international law”, ongoing at that time. Her intellectual interest in learning about the work of early career researchers, and generosity in sharing her time, experience and knowledge with them, have benefited many, including during her term as the President of the Society of International Economic Law. After that initial meeting, we (directly or indirectly) continued our conversations about treaty interpretation, in academic settings as well as hearing rooms at the Centre William Rappard, and deepened our collaboration, for which I am very grateful.

A central part of Gabrielle’s scholarship has focused on the functioning and effects of the WTO dispute settlement system, the principles guiding the interpretation of the WTO covered agreements, and the interface between trade law and non-trade concerns such as environmental and human rights protection. In that scholarship, she has often sought to compare and contrast WTO law with public international law.<fnref n="2" /> A common theme has been the understanding of the choices of panels and the Appellate Body in interpreting the WTO covered agreements. In her academic writings (while building on her practical experience), Gabrielle has considered interpretive practices not solely as a matter of WTO law, but also sought to evaluate those practices from an external perspective—exploring how WTO law and the reports of panels and the Appellate Body have been taken into account by other international courts and tribunals.<fnref n="3" /> For example, in assessing the Appellate Body’s interpretation of “subsequent practice” within the meaning of the *Vienna Convention on the Law of Treaties*<fnref n="4" /> (*VCLT*), she considered that the reference to that understanding in arbitral awards “somewhat promotes an epistemic community around the interpretation of Article 31(3)(b), in which the WTO plays an important role.”<fnref n="5" /> Likewise, she has noted that “the WTO *acquis* has generated a healthy degree of cross-fertilization in the way it has been perceived by other [dispute settlement mechanisms].”<fnref n="6" /> In essence, through her scholarship, she has sought to build bridges between WTO lawyers’ understanding of public international law and public international lawyers’ understanding of WTO law.

Against that background, a particular feature of Gabrielle’s work on treaty interpretation has been her interest in examining the practice of evolutionary interpretation, as a matter of WTO law and public international law. According to Gabrielle, “evolutionary interpretation” is

> not just […] an abstract concept, but […] a meaningful practice embodied in the terms used in a treaty, its social and legal context, the continuation of its object and purpose through time, or the evolution of the law surrounding the instrument under interpretation.<fnref n="7" />

Apart from evolutionary interpretation of the substantive rights and obligations under the WTO covered agreements, she has considered the evolution (and codification) of principles and practices governing WTO dispute settlement, over time.<fnref n="8" /> In part, her own writings have helped to make those practices more visible and understandable.<fnref n="9" />

Gabrielle recognized early on that *US—Shrimp*, where the WTO Appellate Body first expressly mentioned evolutionary interpretation, was not an isolated instance but reflected a broader tension in many legal systems.<fnref n="10" /> In particular, this tension exists between the need for security and predictability of the law and changes over time affecting the interpretation and application of international agreements.<fnref n="11" /> In WTO law, this tension is possibly more visible because the treaty drafters expressly stated that the WTO dispute settlement “is a central element in providing security and predictability to the multilateral trading system,”<fnref n="12" /> must “clarify the existing provisions of those agreements in accordance with customary rules of interpretation of public international law”<fnref n="13" /> but “cannot add to or diminish the rights and obligations provided in the covered agreements.”<fnref n="14" /> Moreover, the WTO covered agreements comprise a complex set of treaties (of which some of the texts date from 1947), concluded for an indefinite period of time<fnref n="15" /> and with an increasing number of parties. In addition, WTO dispute settlement involves continuously revisiting the same treaty texts against the background of rapidly changing trade policies and measures giving effect to those policies as well as of an evolving landscape of international agreements outside the WTO, and the interest to maintain the effectiveness of the WTO agreements.

The principles of treaty interpretation codified in the *VCLT*, as well as other customary principles not codified therein, offer various tools for taking into account legal or factual developments subsequent to a treaty’s conclusion.<fnref n="16" /> Those tools include the text and context of the treaty, the object and purpose of the treaty, subsequent practice and agreements, other rules of international law and even supplementary means of interpretation. However, despite the function of those provisions as a possible basis of evolutionary and other approaches to interpretation, international courts and tribunals exercise a certain degree of discretion in deciding to rely on those elements and possibly, based thereon, to identify or construct the intention of the parties. Whether it is a matter of method of interpretive reasoning or judicial policy, international courts and tribunals do not always make the same interpretive choices including in respect of the question of whether to take account of factual and legal developments subsequent to the conclusion of the treaty that they have jurisdiction to interpret and apply. Elements outside the principles of treaty interpretation codified in Articles 31 to 33 of the *VCLT* might also affect interpretive choices. Therefore, factors explaining how that discretion is exercised, taking into account the principles of treaty interpretation codified in Articles 31 to 33 of the *VCLT*, are relevant too in understanding the reasons for the choice for or against evolutionary interpretation. It is not particularly revealing to state that every interpretation of a text with authority as law starts with the wording of that text because that text is the result a consensus. However, that position does not necessarily resolve, for example, how an international court or tribunal in practice moves from one element to another in every case of treaty interpretation and eventually might opt for an evolutionary interpretation. To characterise an interpretation as evolutionary, it is typically assumed that an interpreter can ascertain the treaty’s meaning at the time of its conclusion and the original intention of the parties. With a large set of multilateral agreements such as the WTO covered agreements, having a rich history and a growing set of diverse parties, it appears more difficult to ascertain the so-called original meaning as compared to that of, for example, a bilateral agreement. In that context, Gabrielle has rightly remarked that “[t]he issue of ‘changes’ is particularly relevant in the context of the WTO Treaty, because it combines long-standing provisions with other, more recent ones, adopted simultaneously.”<fnref n="17" />

In light of those considerations, Gabrielle’s scholarship has contributed to moving the discussion beyond a general understanding of evolutionary interpretation to develop a typology of its different categories.<fnref n="18" /> According to this typology, evolutionary interpretation can be understood through various lenses which she considers can all be accommodated under the principles of treaty interpretation,<fnref n="19" /> including linguistic changes (affecting generic terms), the broader context in which the agreements are interpreted, physical or technical transformations relevant to the object and purpose over time, and changes in other relevant treaties or sources of international law.<fnref n="20" /> Through her work, she has signaled that a more nuanced approach might be preferable, instead of treating evolutionary interpretation as a monolithic concept.<fnref n="21" /> The WTO covered agreements include provisions dating back to 1947 together with newer understandings and agreements. This combination of older and newer provisions necessitates careful consideration of how they are interpreted in light of subsequent developments, including but not limited to subsequent practices and agreements.<fnref n="22" /> Moreover, she has linked evolutionary interpretation to the interest of WTO adjudicators to “maintain the relevance of the rules that they interpret,”<fnref n="23" /> and thus their effectiveness. That understanding was also the basis for the conference on evolutionary interpretation, which Gabrielle co-organised in 2018 at the University of Geneva.

In sum, Gabrielle’s scholarship provides a comprehensive and nuanced understanding of treaty interpretation, with a particular emphasis on evolutionary dimension. Her development of a typology, her grounding of evolutionary interpretation within the framework of the *VCLT*, and her call for coherence in international law have significantly contributed to the field. Her work has constructed a narrative about the interaction between the often static nature of treaty texts and the dynamism of international (trade) relations.

<footnote n="1">On how Gabrielle understood her role as a legal officer at the WTO Secretariat, see Gabrielle Marceau & Akshaya Venkataraman, “Unmasking the Phantom of the Opera: Is There a Hidden Secretariat in the WTO Dispute Settlement System?” (2022) 116 AJIL Unbound 395 [Marceau & Venkataramen, “Unmasking the Phantom of the Opera”].</footnote>

<footnote n="2">See e.g., Gabrielle Marceau, Rebecca Walker & Niki Koumadoraki, “Silence in WTO” (2022) 56:2 J World Trade187 [Marceau, Walker & Koumadoraki, “Silence in WTO”]; Gabrielle Marceau & Clément Marquet, “Practices and Ways of Doing Things in the World Trade Organization (WTO) Law” in Hélène Ruiz-Fabri, ed, *International Law and Litigation: A Look into Procedure* (Baden-Baden: Nomos, 2019) 513 [Marceau & Marquet, “Practices and Ways of Doing Things in the WTO”].</footnote>

<footnote n="3">Gabrielle Marceau, Arnau Izaguerri & Vladyslav Lanovoy, “The WTO’s Influence on Other Dispute Settlement Mechanisms: A Lighthouse in the Storm of Fragmentation” (2013) 47:3 J World Trade 481 [Marceau, Izaguerri & Lanovoy, “The WTO’s Influence on Other Dispute Settlement Mechanisms”].</footnote>

<footnote n="4">*Vienna Convention on the Law of Treaties,*23 May 1969, 1155 UNTS 331</footnote>

<footnote n="5">Marceau & Marquet, “Practices and Ways of Doing Things in the WTO”, *supra* note 2 at 533.</footnote>

<footnote n="6">Marceau, Izaguerri & Lanovoy, “The WTO’s Influence on Other Dispute Settlement Mechanisms”, *supra* note 3 at 532.</footnote>

<footnote n="7">Gabrielle Marceau, “Preface” in Georges Abi-Saab, Kenneth Keith, Gabrielle Marceau & Clément Marquet, eds, *Evolutionary Interpretation and International Law* (Oxford: Hart, 2019) v at vi [Marceau, “Preface”]. This edited collection includes papers presented at a 2018 conference on evolutionary interpretation co-organised by Gabrielle.</footnote>

<footnote n="8">Marceau & Marquet, “Practices and Ways of Doing Things in the WTO”, *supra* note 2.</footnote>

<footnote n="9">See e.g., Gabrielle Marceau, Catherine Quinn & Juan Pablo Moya Hoyos, “Judging from Venus: A Response to Joost Pauwelyn” (2015) 109 AJIL Unbound 288; Marceau & Venkataraman, “Unmasking the Phantom of the Opera”, *supra* note 1; Marceau, Walker & Koumadoraki, “Silence in WTO” *supra* note 2; Marceau, Izaguerri & Lanovoy, “The WTO’s Influence on Other Dispute Settlement Mechanisms”, *supra* note 3. Gabrielle Marceau & Jennifer Morrisey, “Clarifications of the DSU brought by WTO jurisprudence” in Joseph A McMahon, ed, *Trade and agriculture: negotiating a new agreement?*(London: Cameron May, 2001) 143.</footnote>

<footnote n="10">Marceau, “Preface”, *supra* note 7 at v.</footnote>

<footnote n="11">*Ibid*.</footnote>

<footnote n="12">WTO, *Understanding on Rules and Procedures Governing the Settlement of Disputes*, WTO Doc LT/UR/A-2/DS/U/1 (1994), art 3.2, online: <docsonline.wto.org> [perma.cc/DYX8-9FFY].</footnote>

<footnote n="13">*Ibid*.</footnote>

<footnote n="14">*Ibid*.</footnote>

<footnote n="15">See e.g., WTO,*China—Measures Affecting Trading Rights and Distribution Services for Certain Publications and Audiovisual Entertainment Products*, WTO Doc WT/DS363/AB/R (2010) at para 396, online: <docs.wto.org> [perma.cc/KK5D-YXPY]: “More generally, we consider that the terms used in China’s GATS Schedule (‘sound recording’ and ‘distribution’) are sufficiently generic that what they apply to may change over time. In this respect, we note that GATS Schedules, like the GATS itself and all WTO agreements, constitute multilateral treaties with continuing obligations that WTO Members entered into for an indefinite period of time, regardless of whether they were original Members or acceded after 1995.”</footnote>

<footnote n="16">This paragraph is based on Isabelle Van Damme, “Understanding the Choice for Evolutionary Interpretation” in Georges Abi-Saab, Kenneth Keith, Gabrielle Marceau & Clément Marquet, eds, *Evolutionary Interpretation and International Law* (Oxford: Hart, 2019) 171, esp 172—73.</footnote>

<footnote n="17">Gabrielle Marceau, “Evolutive Interpretation by the WTO Adjudicator” (2018) 21 J Intl Econ L 791 at 792. [Marceau, “Evolutive Interpretation by the WTO Adjudicator”].</footnote>

<footnote n="18">*Ibid*.</footnote>

<footnote n="19">*Ibid* at 812.</footnote>

<footnote n="20">*Ibid* at 793.</footnote>

<footnote n="21">*Ibid*.</footnote>

<footnote n="22">Marceau & Marquet, “Practices and Ways of Doing Things in the WTO”, *supra* note 2 at 531—37.</footnote>

<footnote n="23">Marceau, “Evolutive Interpretation by the WTO Adjudicator”, *supra* note 17 at 813.</footnote>