When it first encountered the Genocide Convention in its 1951 Advisory Opinion, the International Court of Justice recognized that the treaty reflected the ‘most elementary principles of morality’. Its provisions were to be read broadly, in light of the Convention's transcendent object and purpose. This expansive approach stands in contrast with the narrow interpretation of Article IX in the recent Judgment in Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Croatia v. Serbia) case. This article is a commentary on the retroactive obligation to punish genocide under the Convention with regard to acts occurring prior to its entry into force for that state. It concludes that the Court's narrow interpretation of its jurisdiction ratione temporis raises wider questions for its contemporary jurisprudence, namely, whether it will interpret human rights treaties enshrining fundamental values any differently than other international instruments.