Objectives This review examined the impact of therapist attachment style on therapeutic alliance and outcomes. Methods Systematic search procedures yielded 11 studies for inclusion that measured associations between therapist attachment style and alliance and/or outcome. Results There is some preliminary evidence that therapist attachment style and interactions between therapist and client attachment style contribute to alliance and therapy outcomes. However, methodological weaknesses and heterogeneity across studies highlight the need for more rigorously designed research in this area. Conclusions There is sufficient evidence to suggest that therapists need to pay attention to the influence of their own attachment style in therapeutic processes and that there is merit in pursing this area of research further. The review is important in highlighting key design issues to consider in future studies. Copyright © 2014 John Wiley & Sons, Ltd. Key Practitioner Message Therapist attachment style has the potential to influence therapeutic alliance and client outcome.Improvements in therapeutic practice might be achieved if therapists have greater knowledge of their own attachment styles and how these interact with their clients' attachment styles to influence the psychotherapy relationship and outcomes.From the outset of their careers, therapists should receive training and supervision to enhance the awareness of their individual attachment experiences and how these play out during the therapeutic process.