He has published several monographs and articles on the topics, some of the most important ones being The Concept of Treaty in International Law (1996), Treaty Conflict and the European Union (2008), An Introduction to International Organizations Law 3rd ed.
Hän on julkaissut aiheista useita kirjoja ja artikkeleita, joista merkittävimpiä ovat muun muassa The Concept of Treaty in International Law (1996), Treaty Conflict and the European Union (2008), An Introduction to International Institutional Law (2nd ed.