In psychology a complex is generally an important group of unconscious associations, or a strong unconscious impulse lying behind an individual's otherwise mysterious condition: the detail varies widely from theory to theory. However their existence is quite widely agreed upon in the area of depth psychology at least, being instrumental in the systems of both Freud and Jung. They are generally a way of mapping the psyche, and are crucial theoretical items of common reference to be found in therapy.

The term "complex" was coined by Carl Jung when he was still a follower of Sigmund Freud. He described them as being 'nodes' in the unconscious. If a trauma from childhood, say, is still affecting a patient, then the behaviours, thoughts, and dreams of the individual could well still be under the influence of a complex developed in their formative years. Freud utilised the idea in his theory of the Oedipus complex, his most famous (and outside of psychology - infamous) psychological formulation. Once Jung broke from Freud and the two men went their own ways, forming their own disciplines behind them, there was briefly a movement in some of Freud's circle to remove all of Jung's work and terminology from their school of psychoanalysis. Freud himself however refused, and so the name 'complex' stayed.

Proposed psychological complexes:

Freudian: Oedipus complex

Jungian: anima animus puer senex

Other: Inferiority complex Napoleon complex