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How to find us prof. dr. P. (Panos) Merkouris

prof. dr. P. Merkouris

Professor, Chair on Interpretation & Dispute Settlement in International Law
prof. dr. P. Merkouris


  • TRICI-Law Project
  • Academic Research Focus & Output                                   

                                   TRICI-Law Project

The TRICI-Law project (the acronym stands for “The Rules of Interpretation of Customary International Law”) is a 5-year European Research Council Starting Grant project. 

You can find more information on TRICI-Law at the project’s website. If you are interested in attending events, or keeping up to date, you can follow us on Twitter, or Facebook, watch videos or podcasts from previous conferences/workshops on our Youtube Channel, or Podcasts channel and download relevant papers written in the context of the project in our Research Paper Series.

The project aims to prove that customary international law is open to interpretation, just as treaty rules are. Moreover, it aims to demonstrate that the process of interpretation of customary international law, which is an unwritten source of law, follows certain rules that can be induced from the case law of international courts and tribunals. The TRICI-Law Project is organized in four working packages, which are described in more detail in the ‘Research’ section of the TRICI-Law website.

In international law, interpretation is ubiquitous and is the process through which the interpreter attempts to determine the true meaning of the rule that is being interpreted. Most cases brought before international courts and tribunals deal one way or another with questions of interpretation. This process has been codified in Articles 31-33 of the Vienna Convention on the Law of Treaties (VCLT). Based on these articles, some of the elements that are taken into consideration are the text, and context of the treaty, its object and purpose and the intention of the parties. However, a key issue is that these VCLT articles refer only to interpretation of treaties and not of Customary International Law.

Customary international law (CIL) , in turn, is one of the formal sources of international law and together with treaties are the most important ones, creating binding rules of international law. Some of the most crucial rules of international law started and continue to exist as CIL. The issue with CIL, however, is that it is an unwritten source of international law. Its existence is determined inductively through examination of two elements, state practice and opinio juris (acceptance as law).

Whereas in the application of treaties the process of interpretation is one that always yields a solution, with respect to CIL these rules of interpretation have not been examined. This leads to one of the following two paradoxical scenarios. Either CIL needs to be induced each and every time, by reference to state practice and opinio juris (but this is extremely problematic as it fails to take into account the continued existence, development and manifestation of CIL rules); or, even worse, CIL is asserted by international judges.

But assertion, essentially means that international judges create law: they become law-makers and exercise a power to legislate (pouvoir de légiférer). Evidently in the study of CIL there is a critical gap in understanding how CIL can be applied in individual cases once it has been formed. TRICI-Law thus aims to prove that even in the case of this unwritten source, i.e. customary international law (CIL), there are rules of interpretation similar to those that exist for the interpretation of treaties, and to determine the content of these rules.

 The four Working Packages (WPs) are:

  •  WP 1 will examine the theoretical validity of CIL being open to interpretation. It will do so by examining international legal theory with respect to both CIL and interpretation. It will provide answers as to whether and why doctrine and domestic legal practice allow or disallow the possibility of interpretation of CIL. In the latter scenario, alternative procedures will be identified that can account for the gap that is currently observed in international judicial practice.
  •  WP 2 will examine the case-law of international judicial and quasi-judicial bodies, in order to induce from it the rules of interpretation of CIL and their precise content. It will provide answers not only as to the exact content of these rules, but also as to their nature. These rules of interpretation may be legal stricto sensu, but they may also be principles/approaches/maxims/rules of logic, which also have content but may not be binding per se on the interpreter.
  •  WP 3 will examine points of convergence/divergence between the rules of interpretation of CIL and those of treaties and of unilateral acts. It will provide answers as to what the similarities and the differences are in both the nature and the content of these rules and inquire into the reasons that may explain these points of convergence/divergence.
  •  WP4 will be a synthesis WP, bringing together all the findings of the previous WPs, and condense them in a single, user-friendly document. That document will be in the form of articles/guidelines on interpretation of CIL and will be accompanied by a more extensive article-by-article commentary.



The SOCRATES project is the flagship project of the 2019 Cohort of the Young Academy Groningen. It stands for Scientists Offering Creative Responses and Advice To Enquiring Students.

 In cooperation with the Scholierenacademie the project will enhance the interaction and ties between RUG scientists from all fields and high-school students in the Netherlands, and aims to spark interest in and passion for science in young minds. The project is currently being developed in close cooperation between the YAG Cohort of 2019 and the Scholierenacademie, and adapted to the current COVID-19 crisis.  


                  Academic Research Focus & Output

My academic research focuses mainly on the sources of international law (ie law of treaties, customary international law and general principles), interpretation and international dispute settlement. Since these are the main building blocks of international law, this allows me to conduct research and publish also in other more specialized areas of international law (eg human rights, environmental law etc).

An overview of my research output, publications (articles, journals, chapters), reports and how these have been cited and referred to by international courts and in international documents can be seen in more detail in the CV Section and the Research Section of my profile page.





Last modified:17 September 2020 11.45 a.m.

Contact information

Oude Kijk in 't Jatstraat 26
9712 EK Groningen
The Netherlands

Department of Transboundary Legal Studies

Job title:
Professor, Chair on Interpretation & Dispute Settlement in International Law
Working hours:
09:00 - 17:00