A pivotal work in the psychological theories of Sigmund Freud, “Three Essays on the Theory of Sexuality” puts forth many of the foundational ideas that make up Freud’s influential theories on sexuality. Freud builds upon his theories of the unconscious that he introduced in “The Interpretation of Dreams” in 1899 and argues that the unconscious mind plays a significant role in sexual behavior and that sexual experiences are a driving force in the development of psychological neuroses and perversions. In this 1905 work, Freud contends that sexual perversion is caused by repression and its root may be found in childhood experiences and not those of adolescence. Freud examines both the abnormal disorders, such as bestiality and pedophilia, as well as the sexual perversions and repressions that can affect otherwise normal and healthy individuals. “Three Essays on the Theory of Sexuality” and its subsequent editions introduced many important ideas into the psychological study of human sexual behavior, such as penis envy, castration anxiety, and the Oedipus complex. Freud believed that sexual abnormalities were some of the most important to study as they affected nearly everyone, from the deeply disturbed to the normally behaved, and his theories have had a far-reaching impact on the field of psychology.