The purpose of this article is to revisit the protracted saga of the International Law Commission Guide to Practice on Reservations to Treaties, as the Special Rapporteur has lived it for nearly 18 years and 16 reports. In the first part, the article recounts the elaboration procedure, pointing in particular to the elements of innovation and flexibility introduced in the process. The principal innovation is the very type of instrument adopted, namely a Guide to practice, and not a set of draft articles that would eventually become a convention. In the second part, the main issues of significant interest for the ILC, as well as for other international bodies and the academic community, are briefly recalled: the question of the unity or diversity of regimes, the permissibility of reservations and the status of the author of an impermissible reservation have been among the most debated issues. Finally, the article explains the structure of the Guide to Practice.

*Please note: This paper was published in the European Journal of International Law, Volume 24, issue 4. It can be found on the EJIL website.