International Law Workshop

Date & time
1.50–4.20pm Thursday 8 March 2018

Finkel Theatre

John Curtin School of Medical Research, 131 Garran Road, The Australian National University


For interstate visitors, we offer suggestions for accommodation near ANU.

Nicole Harman

Presented by the Centre for International & Public Law

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The interaction between treaty and custom

The possible interactions between treaty and custom are generally considered by reference to the well-established framework set out by the International Court of Justice in the North Sea Continental Shelf Cases of 1969; namely, the declaratory, crystallising and generating effects of a treaty (as for a resolution) on a customary rule. The impact of codification on the time it takes for a customary rule to develop, as well as the nature of the substantive rules that treaty codification might generate (obligations of means in addition to those of result; as a consequence of the acceleration in the rule formation process) are also well canvassed. But other issues relative to the treaty-custom interplay warrant consideration today.

With the International Law Commission focussed on the proper identification of customary international law, and separately on the role of subsequent practice in treaty interpretation, one question that arises is how do we differentiate between what might be practice for the purposes of custom as opposed practice for the purposes of treaty interpretation? Each type of practice is different, with its own conditions, thresholds and effects.

Second, some codification issues stand out as being of particular contemporary relevance, even if they are not new. For instance, one can still ask in relation to the ever-flourishing field of international investment law when and whether an investment treaty operates to derogate from or generate customary rules (‘Baxter’s paradox’). Other issues of codification pose practical dilemmas, such as the out-sourcing of codification projects today, especially where the private codifier’s product (such as the NATO Cooperative Cyber Defence Centre for Excellence’s Tallinn Manual 2.0) appears to carry more weight than that of a United Nations organ (specifically, the UN Group of Governmental Experts). Another enduring issue, as ever highlighted by current State behaviour, is the question of custom’s potential scope beyond the treaties when it comes to the laws of armed conflict.

PDF icon Workshop program (731.96 KB) now available.


  • Jesicca Casben Fell »

    A/g Principal Legal Officer, Office of International Law, Attorney-General’s Department

  • Camille Goodman »

    Sir Roland Wilson Foundation Scholar and PhD Candidate, ANU Law School

  • Sarah Heathcote »

    Associate Professor and Deputy Director of the Centre for International & Public Law, ANU Law School

  • Etienne Henry »

    Fellow, Swiss National Science Foundation and CIPL Visiting Fellow, ANU College of Law

  • Marie-Charlotte McKenna »

    Director, International Law Section, Legal Division, Department of Foreign Affairs and Trade

  • Kate Ogg »

    Senior Lecturer, ANU Law School

Additional Materials

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