Lukas Rass-MassonProfessor of Law, Toulouse

Research statement

Past, current and future work.

My research sits at the meeting point of private international law, European law, and the new fields where technology forces classical legal categories to be rethought. Across two decades I have tried to keep one question in view: how do legal orders preserve coherence and justice when the situations they govern cross borders, jurisdictions, and, increasingly, the physical world itself? I come to that question from a German-French vantage point, as a German national whose academic education and career have been spent within the French legal tradition; for me the comparison and coordination of legal orders is lived as much as studied.

Past research

My foundational work is my doctoral thesis, Les fondements du droit international privé européen de la famille (The Foundations of European Private International Family Law), defended at Université Panthéon-Assas in 2015 under the supervision of Yves Lequette. Its claim is that a genuine European private international law of the family is possible, but only if it is built on properly examined foundations: a system that mobilises the full range of private international law methods and articulates them around the choice-of-law rule as its cornerstone. So conceived, European private international law can organise the plurality of national family laws rather than displace it, reconciling free movement and European integration with respect for each national legal order and the values it carries, a pluralist 'unity in diversity' in which coordination, not uniformity, is the aim. The thesis already holds the conviction that has run through my work since: that method is not a technicality but the place where a legal order's values are decided. Well-chosen methods are what make possible the harmonious, articulated coexistence of legal orders, and, in a direction my current research has opened and my future work will pursue, of international and global spaces.

That conviction has organised my methodological work since. In La multilatéralisation des sources du droit international privé (SFDI/Pedone, 2023) I examined how the sources of private international law interact when they multiply; the choice of connecting factor, the treatment of foreign law, and the role assigned to the judge each carry a substantive vision of justice. That last point, the place of the judge in European construction, I set out in the Cahiers de la Justice (2022) as a reflection on the dialogic of European justice, which is built through dialogue between national and European courts, and between legal orders, rather than imposed by hierarchy.

Alongside this I have maintained a sustained engagement with European Union private international law as a living body of rules, most visibly through the annual chronicle on EU private international law in the Journal du droit international (Clunet) and through the co-authored Cours de droit international et européen, revised each year since 2019, to which I contribute a substantial share. Teaching and doctrine here feed each other: keeping the course current forces a yearly reckoning with the state of the field.

I have also worked at the edges of the discipline, such as on European environmental policy, where I contributed a volume examining how EU competence and instruments shape environmental governance.

Current research

My current work is organised around three connected axes.

First, the methodology of private international law. European private international law is where I come from intellectually, and it remains my starting point: I continue the multilateralisation project there, working toward the coordination of overlapping European and international instruments and the coherence of the resulting system. That methodological interest is inseparable from a comparative one, grounded first in the French and German traditions that shaped my formation and remain a constant reference. My other main focus is the comparison between Europe and South-East Asia, a pairing the discipline explores less commonly (most recently on the economic attractiveness of Southeast Asian states, RDAI, 2024); it also takes in the European Union's partnership with Africa (Revue de droit des affaires, 2022). These encounters increasingly ask to be read through a decolonial lens, freeing private international law of its colonial assumptions; I have begun to answer that question through legal humanism, as in my contribution to the Journal of Private International Law conference, 'A humanist foundation for decolonial private international laws?'

Second, the law of the global commons and global spaces. Here I bring private international law to domains that classical categories were not built for. Cyberspace, which I co-direct as a 2026 Centre for Studies and Research at the Hague Academy of International Law with Professor Mohamed S. Helal (Ohio State), is a domain with no territory of its own. The question it raises is not only one of private international law but one about the ordering and operation of the global legal order itself: what counts as normative and as legal, and how legal discourse can be conceived, understood, and developed in spaces that classical categories were not built for. Answering it means moving past the public international law framing that has dominated the debate. Outer space raises the same difficulty for private-law reasoning, on liability, property, and applicable law, when activity occurs beyond any state's territory. Read together, cyberspace and outer space are one problem: how a discipline whose central tool is localisation can order spaces that have none. These spaces are also economic ones, and are fast becoming markets of their own; private international law has long been, among other things, the law of the market, and its task here is to order that activity so that it also serves sustainability and the common good. This is what a law of the global commons both owes to, and demands of, private international law.

Third, law and new technologies. A deliberately multidisciplinary axis that begins with digital law. I have worked on the regulation of digital activities and platforms, from the civil-law tools that discipline them to the questions of jurisdiction and applicable law they raise; the edited volume Enjeux internationaux des activités numériques (Larcier, 2020) gathered much of this and received the Forum International de la Cybersécurité's Prix du livre (Prix de la recherche universitaire) in 2021. The axis already reaches artificial intelligence and law, a strand that will grow, and which I pursue in dialogue with computer scientists and engineers as much as with lawyers, including through doctoral work on the security of information systems (a France–Japan comparison) and on the use of personal data by Fintech and Big Tech.

Future research

Looking ahead, a full-year research leave for 2026-2027 gives me the concentrated time to carry these directions into two projects. The first is a general theory of the common spaces of private international law, the spaces that escape exclusive state appropriation, from cyberspace and outer space to the global spaces thrown up by economic and technological globalisation. Here the connecting factor, the workhorse of the field, loses its footing when there is no territory to connect to. The project's anchor is the Hague Academy Centre on cyberspace and international law; from there I want to build toward a private law of outer space, still largely to be conceptualised, and to test a cross-disciplinary approach between law and geography for grasping global spaces, extending work opened with the Académie des sciences morales et politiques and the Société de géographie in 2025. Running through it are the reconfiguration of the global economy, the growing weight of Southeast Asia, the place of the francophone legal world, and a decolonial reading of private international law in a global frame. The second project, written with François Mailhé, is a systematic treatise on European Union private international law, a body of rules now mature enough to be presented not as an appendage to its parent disciplines but as an autonomous and coherent whole. The two answer to a single ambition: a private law conceived globally and systemically, attentive to the plurality of legal spaces and to the coherence of a discipline in rapid change.

I also expect artificial intelligence and law to move from a current strand into a central one. Artificial intelligence is at once a subject the law must govern and a tool that is already reshaping how legal reasoning is produced, and I want to hold both faces together: the private international law questions that arise once the design and deployment of these systems cross borders, from applicable law and jurisdiction to the allocation of responsibility, and the more reflexive question of what such tools do to legal method and legal discourse, and to the discipline itself. I pursue this in dialogue with computer scientists and engineers as much as with lawyers, in continuity with my work on digital law and with the doctoral research I supervise on the security of information systems and on the use of personal data by Fintech and Big Tech. My own use of these tools in research and teaching is set out on the AI in my work page.

Underlying all of this, I want to develop the humanist foundations of private international law into a project of their own: to work out what a discipline built on respect for the person and for legal pluralism can offer a genuinely plural international and global legal order. A decolonial reading, one that frees private international law of its inherited colonial assumptions, is among the methodological paths I would take to that end. A first application I intend to pursue is transitional justice: how these values, and the rule of law they serve, can help societies confront the legacies of conflict and past injustice. Here the Franco-German reconciliation is the paradigm I know most intimately, a former enmity remade into a shared legal and institutional order, and it shapes how I approach the field. This strand builds on Franco-German collaborative work already under way, and developing it further is a priority for the coming years.

Selected talks

Conferences directed and chaired

Interests: private international law and its methodology; European private international law; comparative private international law, in particular between Europe and South-East Asia; decolonial approaches to private international law; legal humanism and legal philosophy; the law of the global commons and global spaces (cyberspace, outer space); the ordering and operation of the global legal order; law and new technologies, including digital law and artificial intelligence and law; sustainability and the common good; the rule of law; transitional justice.