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The Rules of Interpretation of Customary International Law

Total Cost €


EC-Contrib. €






Project "TRICI-Law" data sheet

The following table provides information about the project.


Organization address
address: Broerstraat 5
postcode: 9712CP

contact info
title: n.a.
name: n.a.
surname: n.a.
function: n.a.
email: n.a.
telephone: n.a.
fax: n.a.

 Coordinator Country Netherlands [NL]
 Project website
 Total cost 1˙480˙708 €
 EC max contribution 1˙480˙708 € (100%)
 Programme 1. H2020-EU.1.1. (EXCELLENT SCIENCE - European Research Council (ERC))
 Code Call ERC-2017-STG
 Funding Scheme ERC-STG
 Starting year 2018
 Duration (year-month-day) from 2018-05-01   to  2023-04-30


Take a look of project's partnership.

# participants  country  role  EC contrib. [€] 


 Project objective

This ERC proposal revolves around the rules of interpretation of customary international law (CIL). CIL along with treaties are the rules most often used in international law. However, whereas rules of interpretation of treaties have been enshrined in Articles 31-33 of the Vienna Convention on the Law of Treaties (VCLT), the rules of interpretation of CIL have not been the subject of critical study. This gap becomes even more pronounced if we consider that interpretation plays a key role in every judicial case, and that one of the basic markers of effectiveness of any legal system is its predictability. By not knowing the rules that govern the interpretation of CIL, we end up playing a ‘game’ the rules of which are unknown, and by consequence predictability is far from guaranteed. Therefore the aim of this project is to determine the existence and to examine the content of the rules of interpretation of customary international law. It will: 1) prove the theoretical validity of CIL being open to interpretation; 2) induce the rules of interpretation of CIL and their content; 3) track the points of convergence/divergence and reasons thereof amongst rules of interpretation of CIL, treaties and unilateral acts as they evolve through time; and 4) create a set of articles/guidelines on the interpretation of CIL. The results will influence the study and theory of CIL; will lead to a re-conceptualization of the theory of sources of international law; will spark a long overdue debate on the interaction between sources of international law; will further our understanding of the process of interpretation and of the basic precepts of the international legal system; and its findings will become the staple point of reference by any ‘user’ of international law. Its ultimate outcomes will clarify the foundations of the international legal system, reduce normative conflict, and provide greater legal certainty and foreseeability in all international law-related interactions.


year authors and title journal last update
List of publications.
2018 Panos Merkouris & Daniel Peat
‘Preliminary Report: The Interpretative Practice of the PCIJ/ICJ\'
published pages: , ISSN: , DOI:
2018 Panos Merkouris & Fay Pazartzis
‘Preliminary Report on The UN Human Rights Committee and other Human Rights Treaty Bodies’
published pages: , ISSN: , DOI:
2020 Panos Merkouris
‘Treaty Interpretation and its Rules: Of Motion through Time, “Time-Will” and “Time-Bubbles”’
published pages: , ISSN: , DOI:
Treaties in Motion: The Evolution of Treaties from Formation to Termination 2020-03-24
2020 Panos Merkouris
‘Termination of Treaties: The Contribution of the Gabčikovo-Nagymaros Judgment’
published pages: , ISSN: , DOI:
The Gabčikovo-Nagymaros Judgment and its Contribution to the Development of International Law 2020-03-24
2019 Panos Merkouris
\'TRICI-Law Project\'
published pages: , ISSN: , DOI:
Groningen Journal of International Law Blog 2020-03-24
2019 Nina Mileva & Marina Fortuna
‘Emerging Voices: The Case for CIL Interpretation–An Argument from Theory and an Argument from Practice’
published pages: , ISSN: , DOI:
Opinio Juris (Blog) 2020-03-24
2020 Nina Mileva
‘The Role of Domestic Courts in the Interpretation of Customary International Law: How can we Learn from Domestic Interpretive Practices?’
published pages: , ISSN: , DOI:
The Theory and Philosophy of Customary International Law and its Interpretation 2020-03-24
2019 Nina Mileva
‘The Under-representation of Third World States in Customary International Law: Can Interpretation Bridge the Gap?’
published pages: , ISSN: , DOI:
ESIL SSRN Research Paper Series 2020-03-24
2018 Fay Pazartzis, Geir Ulfstein, Panos Merkouris & Daniel Peat
‘Interim Report of the ILA Study Group on the Content and Evolution of the Rules of Interpretation’
published pages: , ISSN: , DOI:

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