One of the main disputes in regard to how courts should interpret the federal Constitution pertains to the legitimacy of relying on international law in constitutional interpretation. This Article examines the interpretative status of international law, in general, and the controversy over the use of international law in constitutional interpretation, in particular. The Article offers an innovative approach to the controversy based on the significant difference between customary international law and treaty law; namely, that constitutional interpretation with reference to international law should be limited to customary international law, as opposed to treaty law.