Whether a general rule on omission exists in international criminal law has long been fraught with controversy. It has recently met with increasing acceptance, most prominently by the ICTY Appeals Chamber's judgement of 5 May 2009 (Prosecutor v. Mrkšić et al.). In view of the likely further consolidation of the law, this study deals with the material requirements of 'commission by omission' more comprehensively. It tests several possible ways to give meaning to the offender's duty to prevent the incriminated action, as the 'duty to act' is widely seen as the key to criminal liability for omission. In particular, the present article challenges the prevailing trend in international case law and scholarship to derive individual duties to act from duties under international humanitarian law or domestic law. The alternative approach put forward herein is to derive duties to act genuinely from international criminal law. This is done by extending the 'principle of control', which according to ICC case law constitutes the underlying base for 'commission by action', to the sphere of omission. There, the overarching criterion of control can be broken down into a set of clear-cut duties to act and thus be reconciled with the requirements of legal certainty. Eventually, it is shown that pursuant to the present approach 'commission by omission', albeit not explicitly contemplated by the ICC Statute, falls within the jurisdiction of the ICC.