"Psychology of the Unconscious" by C. G. Jung is a psychological work first published in 1911-1912. Jung analyzes the vivid fantasies of an American woman he never met, exploring their mythological significance and what they reveal about the unconscious mind. The work marks a crucial theoretical split from Freud over the nature of libido, ultimately ending their friendship. Jung later acknowledged he was unconsciously examining his own psyche through this analysis. The book was thoroughly revised in 1952 as "Symbols of Transformation."