Three broad categories of risk and protective factors and the characteristics most strongly associated with later delinquent behavior are: individual (childhood opposition, aggression and hyperactivity, low IQ, inattentiveness, poor school performance), family (parental deviance rejection and discord, ineffective discipline and poor supervision) and environmental (poor, disorganized neighborhoods, where criminality is higher, schools less well organized, and association with deviant peers more likely). The task of developmentalists is to determine the causal relations between these factors, identify those amenable to change and identify the changes with the most impact on preventing delinquency. Delinquency prevention experiments with young persons not referred by the courts tend to be successful mainly when the intervention aims at more than one risk factor, lasts for a relatively long period of time (at least 1 year), and is implemented before adolescence. Figure, table, references