The purpose of this paper is to synthesize and summarize the basic conclusions of literature concerning the effects of day care on infants and young children. The first section of the document briefly indicates limitations of day care research. The second section offers research-based generalizations concerning the effects of day care on intellectual, emotional, social, and physical development (including health and safety). The third section focuses on comparisons between center and family day care; research reviewed indicates that the most critical day care variable is program quality. The fourth section reviews findings of research related to components of quality day care, such as group size, child/staff ratio, caregiver qualifications, caregiver continuity, curriculum, physical environment, and parent involvement. The fifth section points out implications of findings for caregivers, administrators, parents, social policy, legislation, and researchers. A table summarizes and comments on 16 studies comparing effects and characteristics of center day care and family day care. In addition, recommendations for controlling communicable diseases in day care facilities are appended. (RH)