The Rome Statute of the International Criminal Court defines more than ninety crimes that fall within the Court's jurisdiction: genocide, crimes against humanity, war crimes and aggression. How these crimes are interpreted contributes to findings of individual criminal liability, and moreover impacts upon the perceived legitimacy of the Court. And yet, to date, there is no agreed approach to interpreting these definitions. This book offers practitioners and scholars a guiding principle, arguments and aids necessary for the interpretation of international crimes. Leena Grover surveys the jurisprudence of the ICTY and ICTR before presenting a model of interpretive reasoning that integrates the guidance within the Rome Statute itself with Articles 31-33 of the Vienna Convention on the Law of Treaties.