This proposal focuses on emotional development in infancy, and in particular the positive emotions, by pursuing three related objectives: (1) To study positive emotional development in the context of social interaction. We will examine the role of emotions in the establishment of parent-infant relationships and the role of the relationship in the joint regulation of emotions. (2) To examine the developmental origins of individual differences in emotions and their regulation. (3) To focus on social actions during transitions between emotions as a window into dynamic processed. Part of this project involves the continuing analysis of a longitudinal corpus of videotapes made of mother-infant interactions in which each pair was observed weekly during the first year of life. In coding these data we can examine the context specificity of emotions, their relations to ongoing behavioral sequences, and whether the history of the long-term mother-infant relationship influences the emotional process. The other part of the project involves experimental manipulation of emotional processes in longitudinal and cross-sectional samples of infants during the first two years of life. Rather than examine differences in emotions between different settings or conditions (i.e., the presence or absence of mother), we will manipulate features of the mother's behavior, and the sequence of actions that are hypothesized to affect positive emotion. This dynamic, process approach to emotions, coupled with a focus on individual, social and developmental factors, is likely to have implications for the understanding of normal and disturbed emotional and emotion regulatory processes.