This Festschrift honours Professor Detlev Vagts and celebrates his profound scholarly contributions to and influence on the study and practice of transnational law over the last half-century.

On the occasion of his recent retirement from the Harvard Law School faculty and his eightieth birthday, the book brings together a wide range of leading scholars and practitioners from around the globe with a personal connection to the honouree: his colleagues at Harvard Law School and the American Society of International Law (ASIL, especially its Journal), as well as academics, judges and practitioners, many of them former students of Detlev Vagts, with whom his rich life and career have intersected. The book spans the entire spectrum of modern transnational law.

Soon after graduating from law school, Detlev Vagts realised that in the new reality of international relations, law may more readily be understood as extending beyond the classical State system. Philip Jessup, in his famous Storrs Lectures at Yale in 1956, labelled this phenomenon ‘transnational law’, which he defined as ‘all law which regulates actions or events that transcend national frontiers. Both public and private international law are included, as are other rules which do not wholly fit into such standard categories.’ The increasing mobility of people, capital and goods required an expansion of the legal horizon beyond classical public international law and a State-centred view of norm-making. Since then, transnational law has moved to the centre of the law curriculum everywhere.

Introduction

This chapter highlights aspects of the process of diffusion of law as derived from the law and practice of the International Court of Justice (ICJ), the principal judicial organ of the United Nations seated at The Hague in The Netherlands. The ICJ is the world's only court having general jurisdiction over disputes between sovereign States. Diffusion of law is inherent in the concept of transnational law, which likewise is informed by interaction between legal systems and legal traditions. As understood here, legal diffusion essentially is a transnational phenomenon. This chapter seeks to increase our understanding of this phenomenon by focusing on the ICJ. Our focus on the ICJ in illustrating how legal diffusion occurs on the international plane comports with the goal to give ‘increased attention to public international law and institutions’ advocated by the casebook on Transnational Legal Problems for which Detlev Vagts has served as primary author/editor. According to that seminal work, the domain of transnational law is formed by international law and institutions together with aspects of national legal systems concerning ‘matters foreign’. As such, these constituent elements form ‘the legal framework bearing on relationships among nations or among their citizens and business entities’. Nations, citizens and businesses are all affected by the ICJ's work and they play various roles in it, as described below.