This chapter considers the lost legacy of the concept of criminal organizations in international criminal law. When the notion of declaring the criminality of organizations, in addition to determining the guilt of individuals, was first proposed in anticipation of the trial before the International Military Tribunal at Nuremberg, organizational criminality was viewed as an opportunity both to recognize the role of organizations in nurturing mass criminality and to facilitate the prosecution of masses of individuals. But by the time the Tribunal was in operation, the first of these goals had faded away, and organizational criminality represented nothing more than a tool to accomplish individual criminality. This chapter argues that treating criminal organizations as a means to secure individual criminal liability represents a loss, a missed opportunity, in international criminal law. The condemnation of organizations that can attend organizational liability could have created within international criminal law an opportunity to expose the role of organizations in the perpetration of mass atrocity, to call attention to and analyze the institutionalized nature of mass atrocity crimes, which makes these crimes not only unthinkably destructive, but also inherently and importantly distinct from criminal wrongdoing in which a person’s conduct diverges from the standards of most of society. The missed opportunity of abandoning criminal organizations liability is particularly acute, this chapter contends, in light of the research in the decades since Nuremberg establishing how organizations affect individual behaviour. With greater understanding about the mechanisms for individuals’ desire to conform with peers, to obey authorities, and to rationalize their own actions, we can now see that organizations contribute to individuals’ decisions to commit crimes by providing forums and creating environments in which individuals come to believe that criminal behaviour is necessary or normal or even good, or in which individuals fail to recognize their own part in a criminal system. The organizations thus provide not only the machinery for atrocity, but also the motivation. By abandoning the substantive core of criminal organizations, international criminal law fails to identify the foundational role of organizations in creating mass atrocity crimes.