The Adult Attachment Interview (AAI), developed and extensively tested in the domain of developmental psychology, has relevance to psychotherapy research. The authors compare and contrast the ways that social psychologists and developmental psychologists have operationalized the concept of attachment security and discuss corresponding implications for psychotherapy research. In addition, they provide an overview of the AAI and its development, reliability, and validation in developmental psychology and summarize recent work linking AAI responses with distinctive types of psychopathology. A summary of recent work showing the AAI to be a useful indicator of positive outcome in psychotherapy for adults with diverse problems, including depression, borderline personality disorder, and posttraumatic stress disorder, is provided.