The article revisits the Barcelona Traction judgment of the International Court of Justice, rendered forty years ago. It evaluates the lasting influence of the Court's pronouncements on the nationality of corporations and on obligations erga omnes, and uses the case to illustrate the Court's role as an influential agent of legal development. In this respect, it identifies a number of factors that can help to explain under which circumstances judicial pronouncements are likely to shape the law. Copyright © Foundation of the Leiden Journal of International Law 2010.