Offers a comprehensive overview of the extensive case law Identifies the varying methodological approaches of four international criminal tribunals (the ICTY, ICTR, SCSL and ECCC)Takes due account of the "dual nature" of international criminal law and the underlying foundations of international law on the one hand and criminal law on the other, as well as the contradictions that exist between these distinct fields of lawOffers clear guidelines on what function the relevant material used by international criminal tribunals when identifying customary international criminal law can fulfill in connection with proving the existence of customary international lawContributes to the discourse on the sources of international law in general