Therapist effects and the relationship between client and therapist have been demonstrated to be powerful predictors of psychotherapy treatment outcomes (Beutler et al., 2003; Duncan, 2010; Wampold & Brown, 2005). The proposed study sought to expand this body of literature by focusing on therapist mindfulness and its relation to the therapeutic relationship. Using the tripartite model of the therapeutic relationship proposed by Gelso and Carter (1985, 1994) as a theoretical framework, relations among therapist mindfulness, meditation experience, countertransference management, the working alliance, and real relationship between client and therapist were explored. Seventy-seven dyads comprised of therapists in training and their supervisors participated. Therapists in training completed self-report measures assessing trait mindfulness, prior meditation experience, and ratings of the real relationship and working alliance for three clients they saw for individual psychotherapy in the past week and with whom they had met for a minimum of five sessions. Supervisors provided ratings of trainee countertransference management ability. Consistent with theory and prior research findings, results demonstrated positive associations among therapist mindfulness, countertransference management, the real relationship, and the working alliance. Evidence for the moderating effects of prior meditation experience was found such that meditation experience strengthened the positive relationships between therapist self-reported mindfulness and supervisor ratings of countertransference management; therapist self-reported mindfulness and therapist ratings of the real relationship, and therapist self-reported mindfulness and therapist ratings of the working alliance. Contrary to hypothesized expectations, countertransference did not mediate the relationship between therapist self-reported mindfulness and therapist ratings of the real and working alliance. Study strengths and limitations along with implications for clinical practice, training, and supervision are discussed.