Repression is the operation by which a person repels and keeps at a distance from consciousness representations (thoughts, images, memories) that are disagreeable because these representations are incompatible with the ego. For Sigmund Freud repression is the privileged mode of defense against the instincts.

Closely linked to the discovery of the unconscious, the notion of repression accompanies all the developments of Freudian theory.

Initially described in conjunction with hysteria, repression plays a major role in other mental disorders as well as in normal psychic activity. It can be considered a "universal" psychic process insofar as it is constitutive of the unconscious, itself conceived of as a separate realm of the psyche.

More generally, repression is one of the defenses (in fact the primary one) mobilized by the mind to deal with conflicts and to protect the ego from the demands of the instincts.