Associations between markers of ostensible psychological characteristics and social and health inequalities are pervasive but difficult to explain. In some cases, there may be causal influence flowing from social and health inequalities to psychological differences, whereas sometimes it may be the other way around. Here, we focus on the possibility that some markers that we often consider as indexing different domains of individual differences may in fact reflect at least partially overlapping genetic and/or phenotypic bases. For example, individual differences in cognitive abilities and educational attainment appear to reflect largely overlapping genetic influences, whereas cognitive abilities and health literacy may be almost identical phenomena at the phenotypic, never mind genetic, level. We make the case for employing molecular genetic data and quantitative genetic techniques to better understand the associations of psychological individual differences with social and health inequalities. We illustrate these arguments by using published findings from the Lothian Birth Cohort and the Generation Scotland studies. We also present novel findings pertaining to longitudinal stability and change in older age personality traits and some correlates of the change, molecular genetic data-based heritability estimates of Neuroticism and Extraversion, and the genetic correlations of these personality traits with markers of social and health inequalities.As people navigate through their lives, they differ from each other in a great variety of more or less interconnected ways. In order to map this complexity, we often create different kinds of quantitative markers and refer to the classes of markers that correlate or appear similar in etiology or function as some unitary domains or traits. For example, we rank people in terms of their educational attainment, occupational prestige, income, and quality of neighborhood and refer to these markers as socioeconomic status (Hagger-Johnson, Mõttus, Craig, Starr, & Deary, 2012). Additionally, we may rank people in various aspects of health, health-related behavior, and knowledge and jointly refer to these markers as social and health inequalities. On a more psychological side, individuals can be ranked on constructs such as intelligence, personality traits of different breadth and flavor, wellbeing, motivation, attitudes, and the like. Each of these markers is supposed to denote a domain of people's lives, whereas the borders and interfaces between these domains are often unknown and may sometimes be arbitrary.What we are then interested in is whether and how these different domains relate to each other and (co)develop over time. For example, social and health inequalities, which are ubiquitously interconnected (Mackenbach et al., 2008), may influence psychological differences, or the other way around. Moreover, the influence may flow in both directions at the same time (Deary & Johnson, 2010). What is more, the markers that we think of as reflecting distinct domains of ind...