“An analysis of any particular decision of the International Court of Justice sometimes misses broader, cross-cutting themes that animate the Court’s jurisprudence. This essay, prepared for an April 2013 symposium at the European University Institute, Robert Schuman Centre for Advanced Studies, in Florence, explores a few of the themes that emerged from the Court’s 2012 jurisprudence. First, notwithstanding the development of treaty regimes across a broad array of international law, there remains an enduring relevance of customary international law and general principles of law as sources of international law. Second, when identifying rules of customary international law, there is an enduring attraction to analyzing the effects of multilateral treaties in codifying or crystalizing customary rules, rather than relying on a classic analysis of the day-to-day practice of States in conjunction with their opinio juris. Third, the concept of jus cogens remains a powerful feature of international law, available in theory to trump a State’s ability to engage in contrary treaties, yet in practice the concept seems to get little traction; certainly, violations of jus cogens have proven unable to open the door to claims before national and international tribunals. Finally, international law has increasingly become attuned to the rights of persons as against the power of States and international organizations, but the traditional processes of international law pose difficult and sometimes insurmountable hurdles to persons in effectively vindicating those rights.  The Court’s jurisprudence highlights areas of international law that are incomplete or unsatisfactory. The ICJ’s role is not to legislate solutions in those areas, but the Court’s decisions point the direction for changes that might be pursued, either through the development of new treaties or institutions or improvements to those that already exist. Consequently, this essay concludes by suggesting some implications for the future codification and progressive development of international law.”