The book explores the , or the union of opposites, as a psychological process for achieving wholeness.

Mysterium Coniunctionis (1955–56) is the final major work of Swiss psychologist , representing the culmination of over a decade of research into the relationship between alchemy and analytical psychology . Subtitled "An Inquiry into the Separation and Synthesis of Psychic Opposites in Alchemy," it functions as a "splendid capstone" to Jung's career, documenting the discovery of the self through alchemical symbolism. Core Concepts and Symbols