Curiosity is a complex function that is related to a number of other psychological functions such as motivation, arousal, attention, and novelty preference. This paper presents the thesis that curiosity represents a separate ego function which is closely tied to objects and is centrally organizing in all phases of development. It is an integrative function that regulates arousal, motivation, and affect, begins in infancy, has a neurobiological base, and is channeled by the child's social experience. Psychologically, curiosity may serve both libidinal and aggressive aims. Psychoanalytic views of curiosity are considered in light of data from studies of infants' and young children's exploratory activities and a model is presented for the developmental function of curiosity throughout the life-span.