This chapter describes the origins of deterrence theory and problems with the overly narrow conceptualization of deterrence. It discusses the problems within the context of contemporary criminology and criminal justice policy. Many policies rest on weak or inaccurate understanding of deterrence, or are premised on research that has limited generalizability. One example: A great deal of criminal justice policy focuses only on punishment severity as a way of influencing deterrence, but one can increase deterrence in other ways, such as increasing the certainty of punishment or increasing the rewards of non-crime.