On 28 November 2025, CEPANI hosted its annual colloquium, this time dedicated to the complex and pivotal doctrine of res judicata in international arbitration and its application in different jurisdictions. Under the guidance of Dirk De Meulemeester (Honorary President of CEPANI) and Benoît Kohl (President of CEPANI), who both opened and orchestered the colloquium, the event provided a robust comparative approach, featuring insights from numerous national laws including Belgium, France, Switzerland, Germany, the Netherlands, and select common law jurisdictions. The colloquium underscored the arbitration community’s sustained commitment to internationalisation and aimed to provide a platform for inspiring practical solutions to transnational challenges posed by the effects of res judicata.
The foundational presentation was delivered by Jean-François Tossens (Partner, Hanotiau Tossens Goldman), who provided a comprehensive overview of the doctrine of res judicata. He emphasised the fundamental significance of the principle that a final decision should be both conclusive and preclusive for the credibility of any dispute resolution system. While arbitral awards generally enjoy the same res judicata effects as court judgments in many jurisdictions, the practical application in international arbitration is fraught with complexity. This is despite, or perhaps even in particular, because the doctrine is enshrined in international instruments of law like the New York Convention and the Vienna Convention, and further elaborated in soft law, such as the 2006 ILA Recommendations on Lis Pendens and Res Judicata and Arbitration (ILA Recommendations). The central dilemma prompting the debate about the international effects of res judicata is the lack of codification in arbitration rules or laws, forcing practitioners and tribunals to navigate a mosaic of national case law and principles.
It therefore comes as no surprise that the first challenge that arises when a tribunal is tasked with an issue pertaining to res judicata is determining the applicable law. Tribunals frequently resort to national rules to ensure international enforceability, leading to critical choice-of-law questions: should res judicata be governed by the lex contractus or the law of the arbitral seat? And, if so, of which seat – the one of the first arbitration or the one of the second arbitration? Tossens noted that a pragmatic trend favours applying the law of the seat when consecutive arbitrations share the same location. Yet, recourse to national laws might promote fragmented approaches resulting in a lack of consistency and predictability. Indeed, national laws are often ill-suited for international arbitral awards, risking the “contamination” of awards by domestic procedural peculiarities. Tossens concluded with a compelling call for the development of an autonomous international standard to govern res judicata, building upon existing frameworks like the ILA Recommendations.
The heart of the colloquium was a detailed examination of how different legal systems define the scope of res judicata, which, in civil law jurisdictions, is typically centred on the “triple identity” test. As pointed out by Sabrine Schnyder (Independent), this triple-identity test may, upon closer examination, reveal itself as a double-identity test (as in Germany) or truly appear as a four-pronged assessment (as in Switzerland). Yet, the basis remains a common understanding of the significance of the identity of (i) the parties, (ii) the subject matter, and (iii) the cause of action.
In many civil law jurisdictions, the effects of res judicata attach to the award’s operative part and the necessary reasoning supporting it. As examined by Olivier van der Haegen (Partner, Loyens & Loeff) and Maxime Berlingin (Partner, Fieldfisher), in Belgium, awards have immediate res judicata effect upon being rendered, encompassing both negative (precluding re-litigation or re-arbitration) and positive effects (binding decision on the issue). van der Haegen highlighted the immanent value of the Seraing saga for the understanding of res judicata under Belgian law, notably, even before the case reached the ECJ for its prominent judgment rendered this August. Meanwhile, Berlingin noted that Belgian law generally does not consider the violation of res judicata as a ground for setting aside an award for breach of ordre public.
French law, as presented by Benjamin Siino (Partner, Gaillard Banifatemi Shelbaya) and François Bordes (Senior Associate, Gaillard Banifatemi Shelbaya), similarly does not link the doctrine of res judicata to the national (as relevant in domestic cases) or international ordre public. However, Siino noted that court review of a tribunal’s decision on res judicata may be prompted by the prohibition of irreconcilable decisions which, in turn, pertains to the ordre public. A further distinction may be drawn where the res judicata effects of a partial award come into play with Bordes observing that, as per the partial award, the tribunal may become functus officio in respect of the decided matters. Siino and Bordes finally raised the topical question of whether Articles 1506 and 1484 of the Code de procédure civile must be taken to imply that parties may waive the res judicata effects of an award under French law.
Niuscha Bassiri (Partner, ArbBoutique) and Ole Jensen (Managing Counsel, ArbBoutique) noted that, in Germany, the Federal Court of Justice had mentioned in obiter that Parties had the authority to waive the res judicata effects of an arbitral award. Bassiri further elaborated on the German version of the triple-identity test which truly amounts to a double identity test based on the identity of parties and subject matters (whereby the subject matters are determined based on the request for relief and underlying factual matrix). Meanwhile, Jensen observed that, in contrast to the previously examined positions under Belgian and French law, a tribunal’s decision on res judicata is understood to pertain to the German ordre public following a landmark decision of the German Federal Court of Justice in 2018.
The latter is also true under Swiss law. As outlined by Sabrine Schnyder (Independent), Swiss courts consider the tribunal’s assessment of res judicata ex officio whereas arbitral tribunals continue to act only upon party invocation. Schnyder further noted that the Swiss Tribunal Fédéral remains hesitant to apply international standards of res judicata. Indeed, the Swiss Tribunal Fédéral will apply foreign rules of res judicata only to the extent such effects do not exceed those permitted under Swiss law.
The Dutch perspective, presented by Hilde van der Baan (Partner, A&O Shearman) and Guido Straub (Senior Associate, A&O Shearman), offered a diverging view on res judicata both in scope and practical operation. Its scope is not limited to the dispositive but extends to the reasoning that necessarily supports it (excluding obiter dicta). Similar to other civil law approaches, Dutch law is restrictive regarding third-party effects. Indeed, van der Baan and Straub noted that there was no Dutch case law extending res judicata effects beyond the original parties. Although mandatory procedural law in both litigation and arbitration, res judicata must be invoked and, in contrast to Germany and Switzerland, is not part of the national ordre public.
Against the backdrop of the nuanced differences in the application of res judicata in different European civil law systems, Zelda Hunter (Partner, White & Case) and Marius B. Gass (Associate, White & Case) offered a summary of the approaches adopted in select common law jurisdictions. Gass highlighted the three main principles of res judicata in the United Kingdom, namely the cause of action estoppel (preventing re-litigation or re-arbitration of the same claim), the issue estoppel (collateral estoppel in the United States, binding parties on specific issues of fact or law necessarily determined in prior proceedings), and the Henderson principle (Anshun principle in Australia, a broader, procedural doctrine preventing the re-agitation of points that could and should have been raised in the earlier proceeding). Hunter and Gass observed that this common law framework, particularly the Henderson principle, extends beyond the civil law triple-identity test, offering a potentially broader preclusive effect focused on finality.
This comparative examination prompted a forward-looking panel between Erica Stein (Stein Arbitration), Camilla Perera-De Wit (Independent) and Filip de Ly (Professor, Erasmus University Rotterdam) moderated by Benoit Allemeersch (Partner, Quinz). The panel discussed the regulatory basis of res judicata in national law, its application in commercial and investment arbitration and some of the individual principles highlighted. The panel noted that while res judicata is a universally accepted principle, its operation varies profoundly across domestic systems and is heavily reliant on case-specific jurisprudence. The panel observed that the legal basis for applying res judicata in arbitration may be rooted in party autonomy, (partially) allowing parties to choose the applicable procedural rules. This opens the door for soft law instruments like the ILA Recommendations, though their effectiveness was debated.
With regard to the scope of res judicata, Perera-De Wit observed that civil law jurisdictions tend to rely on claims and facts while common law jurisdictions take recourse to broader concepts of cause of action and issue estoppel. Indeed, Perrera-De Wit noted, the underlying principles of party autonomy do not always sit well with the more rigid domestic concepts of res judicata. Against this backdrop, Stein emphasised that domestic practitioners must engage with international developments, as they increasingly inform cross-border practice. The panel further linked the res judicata doctrine to practical concerns in bifurcated arbitrations (where partial awards can create res judicata problems) and in investment arbitration (where concepts like fork-in-the-road provisions are inherently tied to res judicata principles).
The CEPANI colloquium successfully illuminated the intricate tapestry of res judicata in international arbitration. It highlighted a clear tension between the need for finality and legal certainty on the one hand, and the demands of fairness, access to justice, and enforceability on the other, all within a fragmented transnational legal environment. While a fully harmonised international autonomous standard remains an aspirational goal, the comparative dialogue underscored both the common foundations and the persistent national particularities that arbitrators and counsel must navigate. The event reinforced that ongoing scholarly and institutional collaboration is essential to developing more predictable and coherent approaches, thereby strengthening the legitimacy and efficacy of international arbitration as a whole – and, indeed, to prevent that the saga continues.
