Sigmund Freud's Three Contributions to the Theory of Sex is a landmark psychoanalytic study that rethinks sexuality as a force shaping character, mental life, and psychoneurotic illness. Introduced for English-speaking readers by James J. Putnam, it presents Freud's work as part of a larger, interrelated body of thought that must be read as a whole. Grounded in clinical observation rather than speculation, the book challenges the idea that sexuality begins only at puberty or naturally follows a heterosexual pattern, and it insists that childhood is central to adult psychic life. The opening inquiries into sexual aberrations, especially inversion or homosexuality, reject simple labels of degeneration and show how varied, persistent, and historically widespread such cases can be. Freud explores congenital and acquired explanations, the theory of bisexuality, and the separation of sexual object choice from bodily sex traits. He then turns to infantile sexuality, partial impulses, pregenital stages, and the child's theories of birth, castration, and desire, revealing how repression, sublimation, and early conflicts shape both neurosis and civilization itself. This edition has been fully restored with modern typesetting, custom cover design.