There is a recent proliferation of courts and tribunals to prosecute perpetrators of genocide, war crimes, and crimes against humanity. The zenith of this institution-building is the permanent International Criminal Court, which came into force in 2002. Each of these new institutions rests on the foundational premise that it is appropriate to treat the perpetrator of mass atrocity in the same manner that domestic criminal law treats the common criminal. The modalities and rationales of international criminal law are directly borrowed from the domestic criminal law of those states that dominate the international order. In this Article, I challenge this foundational premise. First, I posit that the collective nature of the system criminality of mass violence is qualitatively different than the deviant nature of individual transgressions punished under ordinary domestic criminal law. Accordingly, borrowing from the national to ground the international simply is a convenient, although inappropriate, manifestation of path-dependency. Second, I evaluate the sentences issued by international criminal justice institutions. Surprisingly, although international tribunals have sentenced over 100 offenders over the past five years (and will sentence many more in the immediate future), very little evaluative research has been done on international sentencing. The purpose of this exercise therefore is to build an empirical research agenda with a view to assessing whether the punishment actually inflicted by international tribunals satisfies their avowed deterrent, retributive, and expressive aspirations. Third, based on the evidence, I propose a disarticulation between the effects of international sentencing and its aspirations. One explanation for this disarticulation is the absence of a sui generis theory of punishment for those who commit mass violence. Although there has been expansive institution-building in international criminal law, there has been little theoretical modeling. Unless the brick and mortar institutions are supported by a robust criminology, penology, and victimology, international criminal law will fall short. This Article then proposes several elements that could form part of this self-supporting theoretical and operational framework.