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Open Access Publication in the Spotlight (May) - 'The Theory, Practice, and Interpretation of Customary International Law'

Date:24 May 2022
Author:Open Access Team
Open access publication in the spotlight: May 2022
Open access publication in the spotlight: May 2022

Each month, the open access team of the University of Groningen Library (UB) puts a recent open access publication by UG authors in the spotlight. This publication is highlighted via social media and the library’s newsletter and website.

The publication in the spotlight for the month of May 2022 is an edited book titled The Theory, Practice, and Interpretation of Customary International Law, edited by Panos Merkouris (Faculty of Law), Jörg Kammerhofer (University of Freiburg) and Noora Arajärvi (Hertie School of Governance, Berlin).


Although customary international law (CIL) has been central to international law from its inception, it is often misunderstood. This edited volume remedies that problem by tracing the history of CIL and provides an in-depth study of its theory, practice, and interpretation. Its chapters tackle the big questions which surround this source of international law such as: what are the rules that regulate the functioning of CIL as a source of international law? Can CIL be interpreted? Where do lines between identification, interpretation, application, and modification of a rule of CIL lie? Using recent developments, this volume revisits old debates and resolves them by proffering new and innovative solutions. With detailed examples from international and national courts, it places CIL in a range of settings to explain, explore and reflect upon this developing and highly significant field. 

We asked editor Panos Merkouris a few questions about the book:

This book is the first to be published in the TRICI-Law book series, published with Cambridge University Press. Why did you choose to publish this volume (and the entire book series) open access?

There was not one specific reason, but rather the cumulative effect of a myriad of reasons. I'll mention a few below, but I am certain that if I re-read this I'll kick myself for forgetting a few. So with that disclaimer, here it goes. First and foremost I have to mention that this publication and the Series in general falls under the TRICI-Law project, a 5-year project that is funded by the European Research Council (ERC). One of the obligations under ERC-funded projects, is that all efforts should be made that output stemming from the project is open access. ERC, naturally, is aware that in the case of articles this is easier, whereas for books/monographs and edited volumes this is not necessarily as easy and actually can be more costly. Hence, the requirement of best efforts.

From a personal standpoint as well, both as a student and as a researcher it has always been frustrating when doing research to not have access to certain books/material that was crucial to my research, either because the library did not have it in print, or it did not have a subscription to  the specific database where this material was available. 

The above, and also my gradually increasing familiarity with open access publications and all the issues connected to it due to the TRICI-Law project, the fact that open access publications are more visible, led me to start playing around with the idea of trying to see if we could make a series work, where some of the TRICI-Law's output would be published completely open access. To turn this from an idea to a reality took several steps (the process is described in more detail in the next questions), but I am thrilled that the first installment in the series is out, and that there are more in the pipeline.

To publish this book open access, the publisher charged a book processing charge (BPC) of approximately £9,500. How did you pay for this, and what do you think of such a fee?

This fee was paid through the funds secured for the TRICI-Law project. I need to note here that in the original budget, out of ignorance and a great deal of naïveté, I relied on the fact that in law, books are rarely published open access, so only a small amount had been allocated in the budget for this task. When I eventually started negotiating an open access book series, this meant that I had to accommodate for the funds needed. In this context I need to thank the Board of the University of Groningen, as it agreed to provide the funds from the overhead of the TRICI-Law project. 

As for the fee itself, it is extremely difficult for a researcher not having secured a grant to be able to make such a publication open access. Researchers at Dutch Universities are in a somewhat privileged position, thanks to the Taverne amendment that allows for short publications (articles, chapters in edited volumes) to be made available open access, which is a great step in the right direction and an important assist to researchers in making their research more visible.

However, Taverne does not cover books in their entirety. Funds to cover such expenses are gradually being established, like the UG open access book fund that was recently introduced, but it is a slow process and, of course, the funds can cover only a small portion of such bigger publications. The hope is, however, that with the gradual shift to open access publishers will also realize that this is the way of the future and that the pricing will also gradually drop. 

How did you experience the publishing process? Was it different from publishing closed access?

There were two main prongs of the publishing process. One was the regular one of getting both the series and the individual books in the series approved and published. In this context the process was identical to publishing closed access. 

As for getting the book series off the ground, that took quite a bit of effort, as this was more of an experiment and it involved a lot of moving pieces. It started with me approaching, during an ESIL Conference, Ms. Finola O' Sullivan from CUP, pitching the idea to her, and discussing whether CUP was interested in the idea of an open access book series. This then led to a period of negotiations regarding the feasibility, format, the contracts, and submitting proposals for both the series as a whole and the first installment in the series.

There are numerous people that contributed to this process, both from the UG side and the CUP side (special shout-out to Ms. Nield and my TRICI-Law team), without whose help and comments this would not have gone through. And naturally, the ERC, and UG, who gave the approval of allocating part of the overhead to cover the costs for this Book Series.

Could you reflect on your experiences with open access and open science in general? 

The TRICI-Law project has been a true crash course in open access for me. It has made me much more aware about the ongoing debate on open access and open science in general, and more alert to the benefits of publishing open access, but also the current state both from the perspective of an individual researcher, the University, and the publishers.

Law has traditionally been a field dominated by "closed access" practices. However, this is  gradually changing. More and more attention is being paid by all actors in the field to the benefits of open access. That is not to say that the situation is ideal or even rosy as it stands. The road ahead is a windy and arduous one, but as Tennyson, more eloquently than I could ever dream of, put it in Ulysses: "Come, my friends, 'T is not too late to seek a newer world ... but strong in will To strive, to seek, to find, and not to yield."      

Useful links:

Funder policies: Most research funding organizations require publications resulting from publicly funded grants to be published open access. Most funders allow article processing charges to be paid from grant money, although conditions apply. See this support page for more information about funder policies.

Open Access Book Fund: The University of Groningen has introduced an open access book fund. UG- and UMCG-affiliated authors can apply for funding to enable the open access publication of their monograph or edited volume.

Taverne amendment: Article 25fa of the Dutch Copyright Act (Auteurswet) grants the author of any short scientific work that is fully or partly financed by Dutch public funds the right to make this work freely available to the public, following ‘a reasonable term’ (6 months) after its publication.


Merkouris, P., Kammerhofer, J., & Arajärvi, N. (Eds.). (2022). The Theory, Practice, and Interpretation of Customary International Law (The Rules of Interpretation of Customary International Law). Cambridge: Cambridge University Press. doi:10.1017/9781009025416  

If you would like us to highlight your open access publication here, please get in touch with us.  

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Open Access Team
The Open Access team of the University of Groningen Library

Link: /openaccess
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