The international criminal justice system, although centred on the International Criminal Court (ICC), is dependent on effective domestic action, including state cooperation with the ICC. The ICC is premised on the concept of complementarity, which means that the primary responsibility for exercising jurisdiction in respect of international crimes rests with national systems. However, there is no comprehensive convention obligating states to criminalise and exercise jurisdiction over such crimes at national level. More importantly, there is no comprehensive convention requiring interstate cooperation to promote the successful investigation of international crimes. This paper assesses two recent initiatives aimed at establishing such a comprehensive convention.