Characterization and definitions vary across cultures, but incest refers to sexual relations between close relatives. Prohibition may be according to custom or morality, and embodied in law. In psychoanalysis, the term is also and especially discussed in terms of fantasy and psychological conflict.
Freud mentioned incest for the first time in his correspondence with Wilhelm Fliess (Draft N, dated May 31, 1897), in which he explained "saintliness" in terms of its impious and anti-social character (1950a). A family primordially promiscuous would be forced to give up incestuous behavior in order to avoid being socially isolated.
Incest subsequently became a central theme in Freud's formulation of the Oedipus complex, defined as a child's conflict between sexual desire for the parent of the opposite sex (the "positive" oedipal complex) and repression of that desire. The theory was put forth in Three Essays on the Theory of Sexuality (1905d) and in Freud's discussion of the case of "Little Hans" (1909b), among other works.
From the start Freud also discussed the incest taboo in an anthropological context, in terms of its role in the evolution of society. The first chapter of Totem and Taboo (1912-13a) was devoted to "the horror of incest" and was based on the work of contemporary ethnologists. For Freud it was important to establish that such a taboo operated in every human society. This view gained some support in the work of later anthropologists, including Claude Lévi-Strauss, who, however, maintained reservations regarding Freud's obligatory corollary, that the Oedipus complex was "universal." (See André Green  for a discussion of Lévi-Strauss's views.)
Freud held that psychic energy which accumulates through repression of sexual gratification, prohibitions owed to the oedipal situation, becomes an essential force propelling the development of civilization, especially through channels of sublimation. In "'Civilized' Sexual Morality and Modern Nervous Illness" (1908d), Freud suggested that repression can also provoke psychological disorders through the "damming-up" of libido (the "actual" neuroses) or by substitute symptom formation (the psychoneuroses). The price of civilized morality is high when repression adversely affects too many individuals and distorts the social fabric; Freud examined these issues in Group Psychology and the Analysis of the Ego (1921c) and in Civilization and Its Discontents (1930a).
The incest theme has received little attention in contemporary psychoanalytic literature; an exception is Paul-Claude Racamier's interesting treatment of the "incestual" (1995).
See also: Ethics; Family romance; Framework of the psychoanalytic treatment; Law and psychoanalysis; Myth of origins; Oedipus complex; Phantom; Privation; Prohibition; Psychology of the Unconscious, The ; Secret; "Some Psychical Consequences of the Anatomical Distinction Between the Sexes"; Tenderness; Totem and Taboo ; Transgression.
Freud, Sigmund. (1905d). Three essays on the theory of sexuality. SE, 7: 123-243.
——. (1909b). Analysis of a phobia in a five-year-old boy. SE, 10: 1-149.
——. (1921c). Group psychology and the analysis of the ego. SE, 18: 65-143.
——. (1908d). "Civilized" sexual morality and modern nervous illness. SE, 9: 177-204.
——. (1912-13a). Totem and taboo. SE, 13: 1-161.
——. (1930a). Civilization and its discontents. SE, 21: 57-145.
——. (1950a ). Draft N. "Impulses, fantasies and symptoms." SE, 1: 173-280.
Green, André. (1995). La Casualité psychique. Paris: Odile Jacob. Propédeutique. La métapsychologie revisitée. Paris: l'Or d'Atalante.
Racamier, Paul-Claude. (1995). L'inceste et l'incestuel. Paris: Éditions du Collège de psychanalyse groupale et familiale.
Simon, Bennett. (1992). Incest—see under "oedipus complex": the history of an error in psychoanalysis. Journal of the American Psychoanalytic Association, 40, 955-988.
Simon, Bennett, and Bullock, Christopher. (1994). Incest and psychoanalysis: Are we ready to fully acknowledge, bear and understand? Journal of the American Psychoanalytic Association, 42, 1261-1282.
"Incest." International Dictionary of Psychoanalysis. . Encyclopedia.com. (July 23, 2018). http://www.encyclopedia.com/psychology/dictionaries-thesauruses-pictures-and-press-releases/incest
"Incest." International Dictionary of Psychoanalysis. . Retrieved July 23, 2018 from Encyclopedia.com: http://www.encyclopedia.com/psychology/dictionaries-thesauruses-pictures-and-press-releases/incest