This article explores some conceptual issues regarding criminalization at the domestic and international levels. It attempts to explain what it means to say that a particular kind of conduct has been criminalized, and considers how the processes of criminalization differ in domestic and international law. In unpacking these issues, the article takes the examples of rape and sex trafficking in domestic and international legal systems, explores whether these offenses are criminalized more broadly in international criminal law as compared to domestic criminal law, and briefly outlines possible explanations for this disparity.