The Rome Statute contains a body of legal standards on elements of the offences, concepts of criminal responsibility and defences of unprecedented detail. Whereas these standards serve the International Criminal Court as normative framework, the principle of complementarity implies that domestic jurisdictions are to take the lead in the adjudication of international crimes.This article addresses the question whether domestic legislators and courts are bound to meticulously apply the international standards, or whether they are left some leeway to apply their own (criminal) law. The article starts with a survey of the actual performance of national jurisdictions. Current international law does not explicitly compel states to copy the international standards; at most one might argue that the codification of international criminal law and the principle of complementarity encourage harmonization.Capitalizing on the concept of 'open texture of law' and the methodology of casuistry, the present author argues that a certain measure of diversity in the interpretation and application of international standards is inevitable and even desirable. However, as a general rule, states have less freedom of interpretation in respect of the elements of crimes than in the application of concepts of responsibility and defences.