Attachment theory has long been at the forefront of research efforts to understand the origins and enduring impact of early parent–child relationships. It has also expanded into a theory of lifespan implications with relevance to problems in developmental psychopathology, early intervention, and mental representation. This review of the expanding research literature on attachment is organized around eight questions: (a) To whom do attachments develop? (b) What are the biological foundations of attachment? (c) How does culture influence attachment and its consequences? (d) What contributes to attachments becoming secure or insecure? (e) How does attachment security change over time? (f) What are the later outcomes of secure or insecure attachments? (g) How does attachment influence thinking and social representations? (h) What are the clinical implications of attachment research? The answers to these questions summarize what has been learned about the importance of early parent–child relationships and identify future research priorities.