The most promising conceptual base for prevention and rehabilitation programs is a social-psychological understanding of criminal conduct. This approach highlights four sets of risk factors: (1) attitudes, thoughts, feelings, interpretations of events, and rationalizations that support antisocial behavior; (2) antisocial associates; (3) history of antisocial behavior; and (4) indicators of an antisocial personality. Critics of psychological assessment and correctional treatment services typically discount positive research findings by using irrational techniques to destroy knowledge and uncritically accept negative findings. Community-based treatment services yield more positive effects than treatment services in correctional facilities. Further, intensive treatment services are best delivered to high- risk cases. The prevalence and frequency of future criminal conduct can be assessed through systematic surveys of risk and need factors in individual offender cases. Treatment approaches should be matched with offender needs, circumstances, and learning styles, and prevention and rehabilitation efforts of service professionals should be actively and directly supported through training and supervision. An active interventionist approach is required in effective prevention and rehabilitation, one informed by the interdisciplinary psychology of criminal conduct.