Developmental psychology, in spite of its dynamic growth, has not, thus far, generated a general theory of human development. Present developmental theories are either cognitive or ontogenetic, or both. All are descriptive. Their powers of explanation are limited. None of them include emotional development. It is argued that a theory of development in order to claim generality must (a) include emotional development, and (b) offer means of explaining, rather than only describing, developmental transformations. A nonontogenetic theory of development, called theory of positive disintegration, appears to fulfill these conditions. It is built on Jacksonian principles of evolution of levels of functioning. The central concept of the theory is that of multilevelness of developmental phenomena. Development is seen to be a function of the level of behavioral organization. The theory defines five levels. Each level constitutes a distinct structure. The dynamic elements of the structure of each level are identified. Positive disintegration is the name for the process by which the structure of a higher level replaces the structure of a lower one. The theory explains different developmental patterns by introducing the concept of developmental potential (DP). Although DP is a purely logical notion, it is given observable dimensions designated as dimensions of mental functioning. There are five of these and they correspond to psychomotor, sensual, imaginational, intellectual, and emotional modes of functioning. The first half of the monograph is devoted to the conceptual structure of the theory. The second half to empirical tests of the theory.