Socioeconomic status (SES), an individual's position in society, is defined by a number of interrelated individual, structural, and environmental factors (e.g., income, education, neighborhood). We have known for some time that an SES-health gradient exists (i.e., low SES associated with poor health, high SES associated with good health) but exactly what it is about SES that gets into the body to shape health is still unclear. Yet, understanding these biological mechanisms will be critical for minimizing the costs of low SES for health as well as maximizing the benefits of high SES for health. This lack of clarity may reflect variations in the measurement of SES, a lack of recognition of factors that influence for whom the SES-health gradient will hold and, until recently, limited availability of epigenetic data. We contend that in order to clarify how SES might get into the body to influence health we should first, determine which indictor(s) of SES, and in which combinations, might work to influence biological mechanisms and second, we should consider whether there might be specific factors that influence for whom SES might get into the body to influence mental and physical health. We believe that psychological well-being is an excellent candidate. The key biological mechanism that we will focus on in these relationships is DNA methylation.