This chapter discusses the current state of research on deterrence, highlighting critical limitations and, again, the need for an approach that can help to advance the field and policy. Review of extant work on specific and general deterrence, objective and perceptual deterrence, experiential effects, and other areas of deterrence scholarship makes clear that additional problems – besides the overly narrow conceptualization of deterrence inherited from the eighteenth-century accounts of it – exist. These problems include a large body of disconnected and inchoate research, the lack of a unifying theory for connecting research findings or generating new questions, incomplete recognition of the elements that inhere in deterrence and their importance to understanding it, limitations in research that derive from the incomplete understanding of deterrence, and the persistent lack of an answer to a basic question: Do legal punishments deter? This state of affairs is what motivated and guided development of the reconceptualized theory of deterrence, comprehensive deterrence theory (CDT), presented in the book.