State responsibility and the International Court of Justice (ICJ) have dominatedmuch of JamesCrawford’s activity during the last two decades. This chapter addresses a question situated at the intersection of these two themes: It evaluates the ICJ’s (as well as the Permanent Court of International Justice’s (PCIJ)) influence on the law of responsibility and asks to what extent has the current law of responsibility been shaped (or even ‘made’) by pronouncements of these two ‘World Courts’?What has been the relative impact of ICJ and PCIJ -compared to other ‘agencies of legal development’,1 and compared to their role in other fields of international law?2 These are the two questions on which this chapter seeks to shed some light. As the topic is huge, the treatment is broadbrush rather than nuanced. But as much of our current debate about responsibility is perhaps too granular, it may be defensible to step back and offer some reflections ‘from a distance’. The topic has been covered before, and there is no shortage of views. ‘The law of responsibility has always been essentially judge-made’, states Alain Pellet in a recent Festschrift contribution. James Crawford admits a little more diversity; according to him, ‘[t]he rules of state responsibility have been derived from cases, from practice, and from often unarticulated instantiations of general legal ideas’. And of course, though curiously missing from the two quotations, there is the United Nations International Law Commission (ILC), which rightly counts work on State responsibility among its major contributions to the codification and progressive development of international law. All these have contributed in some way to our understanding, and Patrick Daillier is no doubt right to emphasise the ‘interdependence of the various sources of law in the complex process of the formulation of the law on international responsibility’. But what are the respective roles played by the various ‘sources’ in the ‘complex process’, and where in particular has the PCIJ’s and ICJ’s jurisprudence made a difference? In order to address these questions, it is necessary to, first, demarcate the field of ‘State responsibility’ before tracing and assessing the two Courts’ contributions to it.