Objectives: This review systematically examines research that investigates changes in adult attachment representations during psychological therapy. Method: Studies from two adult attachment approaches are reviewed (interview and self-report) with the aim of concluding whether psychotherapy can improve attachment representations. To guide the interpretation of findings, the methodological quality of studies is assessed. Results: The results suggest that attachment security increases following therapy, whereas attachment anxiety decreases following therapy. Findings are unclear with regard to attachment avoidance. Improvements are observed across different methodologies, patient groups, therapeutic approaches, and therapy settings. Findings also appear to be consistent across different levels of study quality. Conclusions: Overall, research supports the suggestion that attachment styles may alter during the course of psychotherapy, but further controlled trials are required to confirm this conclusion.