Concepts of regression have evolved over time. Regression originally referred to a process of functional dedifferentiation and retreat to archaic forms of organization and function. Libidinal regression described a return to an earlier instinctual phase codetermined by fixations to prior points of developmental weakness. Within structural theory, ego and superego regression were also noted, without fixation points. Regression could be normal or pathological, differential or global, controlled or uncontrolled, and variably reversible. Historical emphasis on regression in pathogenesis was complemented by concepts of regression in the service of the ego, serving development and serving adaptation. Flexible regression may be contrasted with resistance to regression. Regressive and progressive tendencies are in continuous flux. There are new considerations of regression in the analytic process, and in relation to ego development and object relations. It is doubtful that regression per se promotes the resumption of arrested development.