Repression is a key concept of psychoanalysis, where it is understood as a defense mechanism that "ensures that what is unacceptable to the conscious mind, and would if recalled arouse anxiety, is prevented from entering into it." According to psychoanalytic theory, repression plays a major role in many mental illnesses, and in the psyche of the average person.

American psychologists began to attempt to study repression in the experimental laboratory around 1930. However, psychoanalysts were at first uninterested in attempts to study repression in laboratory settings, and later came to reject them. Most psychoanalysts concluded that such attempts misrepresented the psychoanalytic concept of repression.

The founder of psychoanalysis, Sigmund Freud, in seeking to move away from hypnosis and towards encouraging patients to remember their past in a conscious state, observed that the process was strikingly difficult, and he began to suspect that there was some sort of psychic mechanism intervening to prevent access to consciousness. The intensity of his struggles to get patients to recall past events led him to conclude that there was some force that "prevented them from becoming conscious and compelled them to remain unconscious", and which actively "pushed the pathogenetic experiences in question out of consciousness." Freud gave the name of repression to this hypothetical process. He would later call the theory of repression "the corner-stone on which the whole structure of psychoanalysis rests" ("On the History of the Psycho-Analytic Movement").

The psychologist and founder of pedagogy, Johann Friedrich Herbart, whose ideas had influenced Freud's psychiatry teacher Theodor Meynert, had used the term 'repression' as early as 1824, in a discussion of unconscious ideas competing to get into consciousness.

Freud considered that there was "reason to assume that there is a primal repression, a first phase of repression, which consists in the psychical (ideational) representative of the instinct being denied entrance into the conscious", as well as a second stage of repression, repression proper (an "after-pressure"), which affects mental derivatives of the repressed representative.

In the primary repression phase, "it is highly probable that the immediate precipitating causes of primal repressions are quantitative factors such as ... the earliest outbreaks of anxiety, which are of a very intense kind". The child realizes that acting on some desires may bring anxiety. This anxiety leads to repression of the desire.

When it is internalized, the threat of punishment related to this form of anxiety becomes the superego, which intercedes against the desires of the id (which works on the basis of the pleasure principle). Freud speculated that "it is perhaps the emergence of the super-ego which provides the line of demarcation between primal repression and after-pressure".

Neurosis may occur when the personality develops under the influence of the superego and the pressure of the repressed impulses, leading to behavior that is irrational, self-destructive, or antisocial.