In a little over a century, psychotherapy has grown from an obscure and rare practice to a widely accepted and common professional treatment for psychological and social problems in contemporary Western societies. Psychotherapy is not only widely sought out by private individuals; it has also become ensconced in central institutions, including education, the legal system, health insurance and the armed services. It is practised by a wide variety of professionals, whose qualifications and practices are regulated in many countries. Nevertheless, psychotherapy is not at all unified, with dozens of theoretical approaches that specify a vast array of techniques.

The expansion and professionalization of psychotherapy has raised many questions and critiques. One very general and long-standing debate has been about whether psychotherapy is a science or an art. This issue is particularly important because it contains within it the question of whether psychotherapy is demonstrably efficacious. A related set of questions involves the sources of therapeutic benefits: are psychotherapeutic outcomes due to the techniques or the therapist as a person? Perhaps the deepest set of questions regards what we mean by good psychotherapy. Is it simply a set of techniques that produce specific, measureable outcomes (e.g. symptom reduction), or do people engage in the activities of psychotherapy for the sake of a deeper or richer end that can be described in eudaimonic terms? Various models of therapy have proposed personal growth, maturity, highly specific behavioural changes (e.g. more frequent positive self-descriptions) and symptom reduction.