The proposed project represents a short-term longitudinal study, aimed at evaluating the developmental trajectories of child temperament and parent-child interactions in infancy. Growth curves reflecting the patterns of change in temperament characteristics and aspects of the parent-infant interactions will be examined because of considerable evidence suggesting especially rapid development for these in the first year of life. Reciprocal influences between temperament characteristics and parent-child interaction dynamics will also be addressed. The longitudinal evaluation of temperament proposed in this study will rely on recently developed assessment tools (Infant Behavior Questionnaire-Revised; Gartstein & Rothbart, in press, and a parallel Temperament Laboratory Assessment; Gonzales, Gartstein, Carranza, & Rothbart, 2002), allowing for a multi-method, fine-grained analysis of psychobiologically defined temperament attributes. Parent-child interaction factors (reciprocity, responsivity, sensitivity) will be examined through observations that will be analyzed to produce micro behavioral codes (e.g., parents' and infants' vocalizations, attention toward each other, parents' attempts to stimulate/arouse, etc.; Belsky, Taylor, & Rovine, 1984; Isabella, & Belsky, 1991). The contributions of interactions between temperament characteristics and parent-child interaction factors to child security of attachment, at 12 months of age, will be examined. A number of studies have addressed temperament in infancy, as well as parent-infant interaction dynamics, however, a detailed evaluation of both domains, their reciprocal influences and interactions, has not been undertaken. Thus, the proposed study will add to the understanding of these relationships, and the contributions of temperament and parent-child interaction antecedents of attachment security, described as an important marker in social emotional development. A group of infants and parents (N=200) will be recruited when the infants are 4 months of age, and followed until 12 months of age, participating in 5 evaluations. Temperament and parent child interactions will be evaluated through out the first year of life, with attachment security assessed at 12 months of age.