Abstract
This article investigates the hypothesis that therapists' personal (psychological) maturity is a key factor in therapeutic effectiveness. Maturity is defined in terms of intra- and interpersonal openness, acceptance, and genuineness. Effectiveness is defined in terms of therapeutic process and outcome. The article reviews the literature pertinent to this topic from the standpoint of therapeutic theory and research. Although the results of this review indicate provisional support and far-reaching political and professional implications for the hypothesis, notable limitations in the data preclude a more definitive conclusion.