Deciding what works in the prevention of crime called for applying rigorous means for determining which programs have had a demonstrated impact on the reduction of crime and delinquency. The study concluded that very few operational crime prevention programs have been evaluated by using scientifically recognized standards and methodologies, including repeated tests under similar and different social settings. Based on a review of more than 500 prevention program evaluations that met minimum scientific standards, the report further concluded that there was minimally adequate evidence to establish a provisional list of what works, what doesn't, and what is promising. For infants, frequent home visits by nurses and other professionals are apparently helpful. For preschoolers, classes with weekly home visits by preschool teachers are useful; and for delinquent and at-risk preadolescents, family therapy and parent training have proven promising. Effective school programs encompass organizational development for innovation; the communication and reinforcement of clear, consistent norms; the teaching of social competency skills; and the coaching of high-risk youth in "thinking skills." Vocational training helps older male ex- offenders, and the use of rental housing for drug dealing can be countered with nuisance abatement action on landlords. Extra police patrols are effective for high-crime hot spots, and incarceration and monitoring by specialized police unit can reduce crime by high-risk repeat offenders. Also effective are on-scene arrests for domestic abusers who are employed, rehabilitation programs with risk-focused treatments for convicted offenders, and therapeutic community treatment programs for drug-using offenders in prison. This report summary also describes what types of programs do not work and what programs hold promise.