Psychotherapy is a systematic application of psychological methods within a structured interpersonal relationship between a trained professional and an individual or group, designed to address psychological distress, modify maladaptive patterns, and facilitate personal growth. As a research concept and methodological approach, it investigates the efficacy, mechanisms of change (such as the therapeutic alliance), specific techniques, and diverse applications of these interventions across various populations and conditions, signifying its importance as a primary non-pharmacological intervention for mental health and well-being.