Research from several domains indicates that genetic factors, childhood environment, and later interpersonal experiences are important sources of how patients relate to their therapists (transference). Transference work, a core specific technique in psychodynamic psychotherapy, focuses on exploring the patient-therapist relationship, with the idea that this may lead to improvement of the patients’ relationships outside therapy. Many psychotherapy researchers hold the position that specific techniques do not contribute much to the outcome of psychotherapy. However, more than 30 studies have reported significant associations between transference work and outcome. These findings indicate that transference work interventions are indeed active ingredients (for better or worse). Naturalistic studies suggest that a high frequency of transference interventions may have negative effects. Randomized clinical trials indicate that transference-based treatments and alternative treatments work equally well with regard to symptom improvement. However, transference-based treatments appear to be much more effective with regard to interpersonal relations and other measures of personality functioning. The average between-groups effect size for the experimental studies listed in this article was large. Contrary to common clinical wisdom, transference interventions seem to be most important for (mainly female) patients with difficult interpersonal relationships and more severe personality pathology. Gain of insight may be a specific mechanism of change in dynamic psychotherapy, but only one treatment component study has linked transference work directly to gains in insight and subsequent improvement in interpersonal functioning. Research that examines how transference phenomena may be responded to in nondynamic therapies is scarce.