Regression may not only lead to decline and degeneration, but may also be a necessary phase of retrogenesis. Developmental differentiation and specialization of function may be given up in the service of regaining new potentialities for adjustment. The author uses many examples to discuss regression in the experimental, therapeutic, and catastrophic setting. Regression can be a protective encystation in situations of intolerable stress and lead to regeneration with a feeling of being newborn under favorable circumstances. One can differentiate between phylogenetic regression, in which more archaic biological patterns, and ontogenetic regression, in which more infantile personal patterns are resumed. Many psychosomatic reactions involve both types of regression. Collective versus personal regression and how they relate to sociopolitical problems are discussed.