Although emotion has long been considered important to psychotherapeutic process, empirical assessment of its impact has emerged only recently. The present study applied two meta-analyses to explore the association between therapist expression of emotion and psychotherapy outcome, and client expression of emotion and psychotherapy outcome. Overall, 66 studies (13 for the therapist meta-analysis and 43 for the client meta-analysis) were included. A significant medium effect size was found between the therapist’s emotional expression and outcomes (d = 0.56) and a significant medium-to-large effect size between the client’s emotional expression and outcomes (d = 0.85). Third-party rating of emotional expression emerged as a significant moderator of outcomes. Limitations of the research, diversity considerations, and therapeutic practices that conclude the article are then presented.