This study analyzes the first century of the evolution of international adjudication as a permanent fixture of international society. Through a case study approach, examining specific international courts, Jean Allain seeks to demonstrate the various limitations to effective adjudication on the international plain. By examining the ‘Hague System’ of adjudication, as manifest in the Permanent Court of Arbitration and the World Court, the structural limitation of a system predicated on volunteer acceptance of adjudication is drawn out. Finally, the European Court of Justice is examined to demonstrate that the rule of law can be effectively implemented internationally if States so desire, and that it is simply the intransigence of States, over the last century, which has limited the rule of law on the international plain.