50 Years Vienna Convention on the Law of Treaties


The Vienna Convention on the Law of Treaties (VCLT), adopted in Vienna in 1969, is frequently called the most important instrument governing treaty law, largely codifying customary international law. State and judicial practice are guided by the authoritative rules of the VCLT. Accordingly, over the last five decades, the VCLT has become a “pillar” of the law of treaties. It incorporates crucial rules of the law of treaties, including the interpretation of treaties, reservations, and the competence to conclude treaties.

In other areas, the VCLT rules have perhaps been of lesser practical importance, such as those concerning the invalidity (and termination) of treaties. Although the central importance of the VCLT for the law of treaties is undisputed, opinion differs on the practical relevance of its diverse sections and chapters.

Against this background, a stock-taking in the year of the 50th birthday of the VCLT seems warranted. The Conference on 18 November 2019 takes the VCLT’s anniversary as a starting point to examine selected developments in the law of treaties over the past five decades. The Conference, which is held in Vienna, the city of major international law codification conferences, is organised by August Reinisch and Christina Binder in honour of Karl Zemanek, who played a key role in some of these conferences. Karl Zemanek was Professor of International Law at the University of Vienna for sixty years and celebrates his 90th birthday on 18 November 2019.

Registration (& coffee)

Welcome addresses: Paul Oberhammer,
Dean of the School of Law, University of Vienna
Axel Marschik, Political Director, Austrian Ministry for Europe,
Integration and Foreign Affairs
Helmut Tichy, Legal Adviser, Austrian Ministry for Europe,
Integration and Foreign Affairs

The VCLT 50 years ago: The VCLT Conference 1969
Contemporary witnesses of the negotiations: The Austrian
Delegation –
Hanspeter Neuhold, University of Vienna
Willibald Pahr (tbc), Former Minister of Foreign Affairs

The VCLT over the last 50 years: Developments in the law
of treaties – I
Interpreting the Interpretation of Treaties –
Veronika Bílková, Charles University Prague
Treaties and subsequent practice –
Georg Nolte, Humboldt University Berlin


The VCLT over the last 50 years: Developments in the law of treaties – II
Prospects of the reservation regime of the VCLT –
Catherine Brölmann, University of Amsterdam
Provisional application: A futile exercise? –
Gerhard Hafner, University of Vienna
The VCLT’s rules on treaty termination –
Christina Binder, Bundeswehr University Munich


The VCLT 50 years on: Unresolved questions and lacunae
The eternal question of ius cogens –
Hélène Ruiz Fabri, Max Planck Institute Luxembourg
Dire Tladi, University of Pretoria

16.30-17.00 Concluding remarks: August Reinisch, University of Vienna

17.00 Reception

Dachgeschoß Juridicum (Top Floor)
Schottenbastei 10-16
1010 Wien

Registration by E-Mail to registration.vclt@univie.ac.at