The concept of socioeconomic status (SES) has had a central and longstanding role in the social sciences. In addition to the study of class differences in social status per se, SES has served as a predictor, outcome, or control variable. This chapter addresses the issues such as: nature of the relations among SES factors in a cohort of families studied longitudinally across an interval of almost two decades; pervasiveness of SES to various domains of children's psychological functioning; and relations between SES and children's family environment. In sociology SES has implications for power, prestige, and wealth. For developmental scientists, as the present data reveal, it relates to virtually every aspect of human psychological development and across a considerable period of time. SES permeates almost every component of one's psychological development. One can hardly think of any other variable that is so central in the course of human psychological development.