The authors review the literature on the psychology of sex offenders, variables associated with recidivism, actuarial methods to predict recidivism, and treatment. Sexual deviance measured phallometrically can discriminate, with high accuracy, between sex offenders and other men. Sex offenders remain at risk for a long time after release, and combinations of variables selected for their cumulative efficiency in predicting recidivism have been developed and validated. The ability of any interventions to effect reductions in recidivism is unknown. Methodologically sound evaluations of all intervention (therapy, drugs, community notification, registration, and supervision) should have high priority. Finally, application of the available data can increase the likelihood that new legislation intended to reduce the risk represented by sexual predators will have its intended results.