In Freudian psychoanalytic theory, defence mechanisms are psychological strategies brought into play by various entities to cope with reality and to maintain self-image. Healthy persons normally use different defences throughout life. An ego defence mechanism becomes pathological only when its persistent use leads to maladaptive behavior such that the physical and/or mental health of the individual is adversely affected. The purpose of the Ego Defence Mechanisms is to protect the mind/self/ego from anxiety, social sanctions or to provide a refuge from a situation with which one cannot currently cope.

They are more accurately referred to as ego defence mechanisms, and can thus be categorized as occurring when the id impulses are in conflict with each other, when the id impulses conflict with super-ego values and beliefs, and when an external threat is posed to the ego.