The Rome Statute of the International Criminal Court defines more than ninety crimes that fall within the Court's jurisdiction: genocide, other crimes against humanity, war crimes and aggression. How these crimes are interpreted contributes to findings of individual criminal liability, and moreover affects the perceived legitimacy of the Court. And yet, to date, there is no agreed-upon 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 International Criminal Tribunals for the former Yugoslavia and Rwanda before presenting a model of interpretive reasoning that integrates the guidance within the Rome Statute into articles 31-33 of the Vienna Convention on the Law of Treaties (1969).