In this essay, we describe a new era of public health research in which prevention science principles are combined with genomic science to produce gene × intervention (G × I) research. We note the roles of behavioral and molecular genetics in risk and protective mechanisms for drug use and psychopathology among children and adolescents, and the results of first-generation genetically informed prevention trials are reviewed. We also consider the need for second-generation research that focuses on G × I effects on mediators or intermediate processes. This research can be used to further understanding of etiological processes, to identify individual differences in children's and adolescents' responses to risk, and to increase the precision of prevention programs. We note the caveats about using genetic data to select intervention participants.