ABSTRACT
This chapter demonstrates that treating unilateral acts as estoppels has not made the acts any clearer, that is, more "legalized," than treating them as obligation erga omnes did. The doctrine of unilateral acts has not included precise enough criteria to reliably establish whether these acts are obligations erga omnes or if it was an estoppel. The chapter discusses the assertion that the 1974 decision in the Nuclear Tests Cases was imprecise because the criteria for unilateral acts it promoted, intention, autonomy, and revocation, were not capable of providing reliable guidance as to when these acts were legal. It examines the concept of estoppels in international law and illustrates that estoppels have been considered to be both a substantive and a procedural principle that limited the acts of sovereign states when there has been detrimental reliance on these acts.
