Research was conducted to assess young preschoolers' knowledge of emotion and to explore the relation between children's understanding of emotion and their prosocial behavior. This discussion briefly describes measures devised to investigate knowledge of emotion, and outlines findings. Also discussed are relations between knowledge of emotion and social competence, as rated by teacher and peers. In addition, the discussion covers research in progress that investigates relations between knowledge of emotion and socialization variables, such as the mother's attitudes about emotionality, her expressed emotions, and her discussion of emotion with the child. (RH)