In keeping with the aims of NICHD-RFA (88-HD-08), "Effects of Non-Parental Infant Day Care on Child Development," the proposed study is an attempt to assess and evaluate the effects of infant day care on children's emotional, social, and cognitive development. It follows the psychological and physical progress of 150 children from birth to 3 1/2 years, taking into account and weighing the relative contributions to that progress of the children's constitutional characteristics, their family contexts, and their day-care experiences. It attempts to identify the conditions under which maternal employment in the first year of an infant's life helps or hinders the infant's development. To do so, it draws on a wide range of assessment methods and measures, including observations at home and in the day-care setting, interviews and questionnaires given to the mothers, fathers and other caregivers, and standard assessments of the children's behavior in semi-structured laboratory situations. In addition, children and their parents are observed and interviewed by trained clinical practitioners. The study also relies on multivariate statistical analyses and the unique advantage of a national collaborative sample.