Surprisingly, scholars studying mass atrocity and genocide have frequently sidelined criminological theories and concepts. Other disciplines have addressed these crimes while mostly ignoring criminological insights and theories. In this review, we assess the potential of criminological theories to contribute to explaining and preventing mass atrocities and genocide, highlight criminological insights from the study of these crimes, and unlock the existing criminological knowledge base for application in the context of these crimes. We begin by outlining how mass atrocities and genocide are similar to other crimes that criminologists have routinely studied. We then turn toward frameworks of structural causation, focusing on the state and community levels. Subsequently, we address microlevel theories that inform why individuals commit such violence, ranging from theories of choice, the life course, and techniques of neutralization to social learning theory and theories of desistance from crime. Finally, we address the victims of genocide and mass atrocity, including the factors associated with victim labels and victimhood itself.