Section I describes relevant research and how it contributes to science-based prevention. It examines the ways in which an understanding of substance abuse is guided by theories in several areas: public health, risk and resiliency, family systems, community systems, and environmental change. It presents protective and risk factors as they occur at the level of the individual, family, peers, school, community, and society. Section II focuses on five family-based strategies and the evidence that supports their effectiveness: parent skills training, family skills training, family in-home support, family therapy, and prenatal and early childhood intervention. Section III offers a series of guidelines for implementing family-based programs for practitioners who want to adapt and apply these strategies in their local program. The concluding section looks beyond the family-based strategies to provide an overview of steps that parents can take to improve the family climate in ways that contribute to prevention. One appendix lists resources, including selected family-based programs, and another appendix suggests ways that individuals, both practitioners and the family members with whom they work, can influence larger environmental factors beyond the family that affect substance abuse problems; it addresses policy, enforcement, education, communication, and collaboration.