Externalizing behavior problems characterized by behaviors such as aggression, destruction of property, and stealing are among the most common childhood adjustment problems and the most reliable predictor of adult mental health problems. This chapter briefly reviews the parenting and family factors that have been implicated in the etiology, maintenance, and exacerbation of these problems. A number of variants of the Triple P—Positive Parenting Program have been developed to address these factors, including individual face-to-face, group, and self-help interventions. These variants are described, and the evidence indicating their effectiveness in reducing externalizing behavior problems is reviewed. It is proposed that a multilevel system population approach in which all variants of Triple P are incorporated and delivered simultaneously by existing services has the potential to achieve a population-level decrease in rates of externalizing behavior problems.