Conceptual frameworks for racial/ethnic health disparities are abundant, but many have received insufficient empirical attention. As a result, there are substantial gaps in scientific knowledge and a range of untested hypotheses. Particularly lacking is specificity in behavioral and biological mechanisms for such disparities and their underlying social determinants. Alongside lack of political will and public investment, insufficient clarity in mechanisms has stymied efforts to address racial health disparities. Capitalizing on emergent findings from the Midlife in the United States (MIDUS) study and other longitudinal studies of aging, this chapter evaluates research on health disparities between black and white US adults. Attention is given to candidate behavioral and biological mechanisms as precursors to group differences in morbidity and mortality and to environmental and sociocultural factors that may underlie these mechanisms. Future research topics are discussed, emphasizing those that offer promise with respect to illuminating practical solutions to racial/ethnic health disparities.