Congruence or genuineness is a relational quality that has been highly prized throughout the history of psychotherapy, but of diminished research interest in recent years. In this article, we define and provide examples of this attribute of the therapy relationship and present an original meta-analytic review of the empirical literature showing its relation to improvement. Analysis of 16 studies (k), representing 863 patients (N), resulted in a weighted aggregate ES (r) of .24 (p = .003; 95% CI = .12 to .36). Moderators of the association between congruence and treatment outcome are examined, and limitations of the extant research are discussed as well. In closing, we advance several therapist practices that are likely to foster congruence and thus improve psychotherapy outcomes.