Abstract International criminal law has evolved from abstract ideas of an international criminal jurisdiction in the early twentieth century to encompass a comprehensive set of tribunals, rules, and methods. This article explores the contribution of the common law to the development of international criminal law, drawing on two key historical episodes – the Nuremberg and Tokyo tribunals, and the ad hoc International Criminal Tribunal for the former Yugoslavia (ICTY) and International Criminal Tribunal for Rwanda (ICTR) – to consider the common law’s historic influence over, and relationship to, uncertainty within the system of international criminal law. First, the article highlights how British jurists framed the normative uncertainty vis-à-vis the idea of international criminal justice in their contributions to this Yearbook. Second, it examines the characteristics shared between common law and international criminal law, with a view to appraising the potential relationship of both ‘systems’. Finally, it interrogates the differing treatments of the common law throughout the development of substantive international criminal law over time, considering how judges utilized the common law as they navigated the complex dialectic between ‘statutory’ and ‘judge-made’ law.