50 years The Vienna Convention on the Law of Treaties (VCLT)

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.

Against this background, a stock-taking in the year of the 50th birthday of the VCLT seemed warranted. The Conference on 18 November 2019 took the VCLT’s anniversary as a starting point to examine selected developments in the law of treaties over the past five decades. The Conference, held in Vienna, the city of major international law codification conferences, was organised by August Reinisch and Christina Binder in honour of Karl Zemanek, who played a key role in some of these conferences. Karl Zemanek celebrated his 90th birthday the same day as the conference, on 18 November 2019.

Karl Zemanek was Professor of International Law at the University of Vienna for sixty years, 10 years of which were taught in the LL.M. program International Legal Studies. For this reason a large number of former LL.M. students seized the opportunity to travel to Vienna to congratulate their professor of the workshop "The Law of Treaties" and greet his successor in this LL.M. program, Univ.-Prof. Christina Binder, who has been teaching this course for already three years.