In the history of clinical psychology and psychiatry, troublesome children and adolescents have been referred to with a variety of labels. This chapter focuses on the role of reinforcement in both the early- and late-starter pathways. According to reinforcement theory, anti-social behaviour is learned and practiced within the child's social environment. For many years, parenting practices have been recognized to be among the most powerful predictors of anti-social behavior. The reinforcement theory has also been tested in the context of intervention trials. From a reinforcement point of view, contextual factors, such as family stress and neighbourhood, all affect the microsocial interactions within relationships. Thus, the effects of the larger context on anti-social behaviour are hypothesized, at least in part, to be mediated through the microsocial interactions. A reinforcement model offers a strong tool with which we can address the problems of anti-social behavior.