This chapter identifies well designed preventive trials, assesses their effectiveness and gives examples of successful and unsuccessful interventions in the prevention of conduct problems in children. Preventive interventions may reduce disruptive behaviour through their impact on associations with deviant peers. There are a number of ongoing, large-scale preventive interventions for conduct disorder presently being undertaken. One distinctive preventive intervention study is the Fast Track Project. This project combines a universal programme with an indicated intervention directed toward high-risk children. Another preventive intervention programme is the Better Beginnings, Better Futures project. In this project, universal preventive interventions are delivered by social services in high risk communities, and evaluated by a separate research unit. The available evidence to date, reviewed in the chapter, suggests that conduct disorder can be prevented: some interventions did have substantial positive effects on distal disruptive behaviour outcomes, including externalizing behaviour, aversive behaviour, and delinquency.