Summarizing across all evaluation studies, regardless of their nature, it has been reported that approximately 60 percent of the programs studied reduce recidivism, with the average reduction being 10 percent (cf., Lipsey, 1992). The average reduction in recidivism for appropriate treatments is 25 percent; even better results can be expected under conditions of optimal therapeutic integrity. Therapeutic integrity refers to programs that are appropriate to the clients served and that use types of therapeutic techniques that are known to work. In addition, programs with therapeutic integrity are designed and evaluated by individuals who are well-versed in behavioral interventions; hire staff who have 4-year degrees in a helping profession; further train their staff to adhere to the clinical dimensions of the interventions they administer; and provide intensive service. The chapter further outlines the principles of effective intervention. In an effort to assess correctional programming typically found in government and private correctional agencies, the Correctional Program Assessment Inventory (CPAI) was developed several years ago. The Inventory now consists of several dozen items generated from the "what works" literature. The CPAI assesses programs on six dimensions: program implementation, client preservice assessment, program characteristics, staff characteristics and practices, evaluation, and an "other" category. The CPAI documents the strengths and weaknesses of a program in each of the six dimensions and provides an overall percentage score of program quality. Currently, the CPAI has been applied to approximately 280 offender treatment programs. This chapter concludes by summarizing the results of the CPAI research. Key concepts and terms as well as discussion questions are provided.