Different subgroups of delinquents appear to learn according to different patterns: neurotic delinquents differ little from nondelinquents, but primary psychopaths perform poorly at learning tasks. For the latter, therapeutic methods based on classic aversive conditioning must attempt to increase subjects' sensitivity through drugs, or intensified background or aversive stimulation. However, empirical evidence does not demonstrate that primary psychopaths learn by imitation less effectively than neurotic delinquents and nondelinquents. The effect of material and social reenforcement on delinquents, primary psychopaths in particular, is unclear. Finally, the learning performance of all three groups of delinquents is approximately equal, if the total learning situation is favorably structured. Based on consideration of various forms of behavioral therapy in a closed institutional setting, (i.e., operant conditioning with token reinforcement, model learning, and classical conditioning) as well as forms of treatment in noninstitutional environments (the family, the school, and leisure activities), and in partially institutional arrangements, it is concluded that for the time being behavioral therapy is probably best used in combination with other therapy forms. Behavioral therapy has the advantage over social and psychological therapy that it has a uniform theory of delinquency, uses natural therapeutic forces in the environment of the client, and has a fairly well-developed series of techniques. Furthermore, the significance of behavioral intervention lies in its potential for controlling criminal activities which are difficult to get at therapeutically with other forms of treatment. Tables, notes, and an extensive bibliography of about 500 entries are supplied.