This longitudinal study will address fundamental questions about the development of emotion recognition across the first 6 months of life in human infants. Emotion recognition is critical for the development of social communication and interaction. By examining the ontogeny of infants' developing competencies in emotion recognition, we can establish the typical developmental trajectory and discover whether there are individual differences in infants' ability to recognize expressions of familiar and unfamiliar adults. This study will extend earlier work on emotion recognition by addressing 2 questions: (1) When do young infants become sensitive to emotional signals of others, familiar and unfamiliar? (2) Are differences in family emotionality (e.g., maternal depression) related to individual differences in infants' development of emotion recognition? Infants (N=48) will be tested longitudinally at 2.5, 3.5, 4.5 and 6 months of age. At each age, infants will be shown two filmed facial expressions (happy and sad) side by side, accompanied by a single vocal expression that will match one of the facial expressions. The expressions will be portrayed by mothers, fathers, and unfamiliar adults. Infants' looking preferences and facial expressions will be coded. Information on parent-child involvement and parental emotionality also will be gathered. The results of the proposed study will enhance the knowledge of the role of person familiarity and family dynamics in infants' recognition of the emotional expressions in the first months of life. Results will speak to the significance of interpersonal interactions for the development of emotion understanding in early infancy.