This book traces the developmental, relational, metapsychological theory that emerges from Erich Neumann's writings, while considering the influences of his life circumstances and relationship with Jung. It revisions, reevaluates, and consolidates the emerging theory, in the hope of reviving interest in Neumann's writings, and indicate his importance as a Jungian theoretician. This manuscript shows that Neumann's theory effectively supplements Jung's original writings, and is relevant to both theory and therapeutic practice. It presents Neumann's formulations of psychological development from birth to the advanced stages of individuation process as a synthesis of his various writings. The books The Origins and History of Consciousness, The Great Mother, Jacob and Esau, Depth Psychology and a New Ethic, and The Child are at the center of focus, supported and amplified by some of Neumann's metapsychological Eranos articles.