Although the United States has relied on the ICJ's doctrine of specially-affected states to claim that it and other powerful states in the Global North play a privileged role in the formation of customary international law, the doctrine itself has never been systematically developed by the ICJ or by legal scholars. This article fills that lacuna by addressing two questions: (1) what makes a state "specially affected"?; and (2) what is the importance of a state qualifying as "specially affected" for the formation of custom? It concludes that a theoretically coherent understanding of the doctrine would give states in the Global South significant power over custom formation.