This paper presents an analysis of day care research and practice in the United States from an ecological perspective, examining the impact of day care on the family and society as well as on the child. Part I contains a summary of major conclusions regarding substantive findings of existing day care research and a statement of policy recommendations in the light of available knowledge. Changes in the structure and position of the American family in recent decades are traced and concomitant changes occurring in the development of children are examined. Existing research on day care is analyzed with two considerations in mind: the strengths and limitations of the scientific findings as indicators of the direct effects of day care on child development, and the significance of the existing research for understanding the broader effects of day care. Part II contains the background data and analyses underlying the conclusions presented in Part I. Specific areas examined include: (1) cognitive development, (2) mother-child relationship, (3) social development, and (4) effects of day care on the family. (JMB)