This paper presents an integrative perspective on infant development (based on a consideration of developmental data) which focuses on the function of the smile. From the earliest spontaneous smiles of the newborn period to mature smiling and laughter, a central role was revealed for an excitation (tension)-relaxation process in producing smiles. This notion is complementary to social and cognitive theories of smiling but is more basic in pointing to the function of the smile for the infant and in stressing continuity of smiles following mastery, and smiles following excitation. In unraveling the changing meaning of the smile, a number of developmental principles are revealed, including the following: (1) developmental sequences may be repeated, though in a transformed and elaborated manner; (2) the infant becomes increasingly active in producing and mastering his own experience; (3) social and individual functions of the smile converge in promoting accommodation to and assimilation of novel events; (4) fear and joy, and wariness and smiling have a close functional relationship with respect to novelty; and (5) cognitive and socioemotional aspects of development are inseparable. (Author/GO)