Initial progress has been made in the conceptualization and study of attachment stability over time, and substantial evidence has accumulated on the association between attachment classification and biopsychosocial functioning (including social-emotional competence, cognition, physical health and mental health). The literature supports the intuitive belief that parent-child attachment representations affect infant and child development in a variety of domains and across several developmental periods. There is substantial evidence that children with secure attachments in childhood develop more positive social-emotional competence, cognitive functioning, physical health and mental health, whereas children with insecure attachments are more at risk for negative outcomes in these domains. However, problems still remain in controlling for variables that may affect attachment classification throughout the lifespan (e.g. changes in life circumstances, stress, caregiving) and in determining how these variables influence later outcomes. Findings from this review are discussed in terms of health promotion and prevention, and areas for future research are outlined. (Contains 6 tables.)