Literature about gender differences and their possible origins, and contemporary psychoanalytic formulations of gender, is reviewed. There is a broad consensus among investigators from different fields, and among psychoanalysts of different theoretical persuasions, that the modal female personality tends to be more sociocentric, and the modal male personality more self-centric. These modal personality differences may be qualitative rather than quantitative. The concept of core gender identity, which articulates the psychological root of these differences, is reexamined in the light of contemporary research into constitutional differences in the organization and activation of the brain, and an interactional model of core gender identity as a dynamic evolving phenomenon over the course of the life cycle is proposed.