This article considers the implications for prevention science of recent advances in research on family poverty and children's mental, emotional, and behavioral health. First, we describe definitions of poverty and the conceptual and empirical challenges to estimating the causal effects of poverty on children's mental, emotional, and behavioral health. Second, we offer a conceptual framework that incorporates selection processes that affect who becomes poor as well as mechanisms through which poverty appears to influence child and youth mental health. Third, we use this conceptual framework to selectively review the growing literatures on the mechanisms through which family poverty influences the mental, emotional, and behavioral health of children. We illustrate how a better understanding of the mechanisms of effect by which poverty impacts children's mental, emotional, and behavioral health is valuable in designing effective preventive interventions for those in poverty. Fourth, we describe strategies to directly reduce poverty and the implications of these strategies for prevention. This article is one of three in a special section (see also Biglan, Flay, Embry, & Sandler, 2012; Munoz, Beardslee, & Leykin, 2012) representing an elaboration on a theme for prevention science developed by the 2009 report of the National Research Council and Institute of Medicine. (Contains 1 figure.)