Kiefer presents a comprehensive overview of the key historical concepts of developmental psychology--maturity and maturation. The result of this historical focus is a view of maturity that accounts for both the social forces shaping beliefs and the social consequences of those beliefs. Here is a bridge between developmental psychology, history, and contemporary society. The author begins by presenting his view of the role of ideas in history and the importance of the idea of moral maturity in psychological science, as well as in the process of understanding self. The history of maturity as a moral ideal is presented, beginning with primitive society. Key features of Medieval, Renaissance, Enlightenment, and modern Western society that have influenced ideas of maturity are considered in turn. In part II, Kiefer examines beliefs about the actual process of growth and development from earlier, nonliterate society and into the present. Attempts to unite the philosophic and scientific concepts of development are discussed, such as the Platonic "path of love" as represented by Carol Gilligan, the Aristotelian "path of reason" by Lawrence Kohlberg, and Freud's "path of conflict." Cultural-historical explanations are sought for the particulars of these interplays. In the concluding section, Plato's "four indestructible stages" of maturity and implications of modern life for the attainment of these stages are evaluated. Kiefer makes a plea for an historically self-conscious psychology. By bringing together concepts from anthropology, philosophy, psychology, and history, the author presents a synthetic view of maturing that has fundamental applications in the fields of human development, social gerontology, philosophy, and psychotherapy.