The Research Unit's work on crime prevention and control has occurred in two phases. The first phase was guided by the theory underlying the medico-psychological model and the environmental and learning theory. The policy purpose of research in this phase was the search for effective penal treatment. Research areas in this phase were criminality prediction, classification and typologies, offender treatment experiments, and cross-institutional designs. The evidence of the studies of prediction and classification suggested that, at best, only a modest proportion of the variance in reconviction can be explained by pretreatment factors for any group of offenders, with the most important factors relating to age and history of offending. According to the treatment experiments, there is little if anything to choose between the differing forms of treatment and their longer-term effectiveness in preventing recidivism. Finally, the cross-institutional studies succeeded in identifying some longer-term effects of treatment, but these were small and appeared to be related to misbehavior in the institutions. Levels of misbehavior varied greatly between institutions and were powerfully associated with aspects of institutional environment. Owing to the findings of treatment ineffectiveness in the first phase of research, the second phase of research was launched under the policy purpose of searching for alternative means of crime control. The overarching theories of this second phase deal with situational factors and offender choice, and research is focusing on incapacitation, deterrent sentencing, police effectiveness, and social and situational prevention. About 340 references are provided along with subject and author indexes.