In a political climate which encourages interdependence between States, international law is steadily developing and increasingly becoming a key factor in the organisation of inter-State relations. This concept of interdependence implies a strong commitment by all States to international law and a shared responsibility for its application. Through the ad hoc Committee of Legal Advisers on Public International Law (CAHDI), the Council of Europe contributes to the implementation of public international law and further acts as a catalyst for its development. Indeed, the CAHDI has established itself as an invaluable actor in the development of public international law, functioning notably as the European Observatory of Reservations and Declarations to International Treaties, a unique and flagship function acknowledged today by other regional organisations. The CAHDI also acts as a laboratory and a catalyst for new ideas. This volume, containing thought-provoking essays by former and current Legal Advisers from a wide selection of Council of Europe countries, arose from the conference celebrating the 50th anniversary of the CAHDI meetings and showcases CAHDI's pioneering work.