The therapeutic alliance represents an important variable in explaining the outcome of mental health treatment. In particular, research suggests that mindfulness practice might help therapists to develop skills that are key to a good therapeutic alliance. Although the therapeutic alliance is well-recognised from a clinical perspective, basic quantitative research is still lacking about the neurocognitive mechanisms involved in establishing and maintaining the alliance between individuals. Recent advances in two-person neuroscience research have demonstrated that interpersonal neural synchrony -which may develop between speaker and listener, or parent and child -is a strong predictor of mutual understanding as well as social learning and influence. Further, social cues that improve communication quality and clarify intent effectively modulate levels of interpersonal neural synchrony, suggesting that this neural index is sensitive to dynamic changes in speaker-listener engagement. Given that the therapeutic alliance depends strongly on shared intentionality and mutual engagement between therapist and client, interpersonal neural synchrony may also index the quality and strength of the therapist-client alliance, and predict treatment outcome. If so, this quantitative neural index could provide a useful clinical tool for measuring and understanding the nature and efficacy of the therapeutic alliance. The present paper discusses these hypotheses, presenting preliminary data from a pilot study investigating neural synchrony between clients and therapists in face-to-face and videoconference interactions, comparing therapists who practice mindfulness with therapists without any mindfulness experience.