Clinical psychology includes the scientific study and application of psychology for the purpose of understanding, preventing, and relieving psychologically-based distress or dysfunction and to promote subjective well-being and personal development. Central to its practice are psychological assessment and psychotherapy, although clinical psychologists also engage in research, teaching, consultation, forensic testimony, and program development and administration. In many countries clinical psychology is a regulated mental health profession.

The field is often considered to have begun in 1896 with the opening of the first psychological clinic at the University of Pennsylvania by Lightner Witmer. In the first half of the 20th century, clinical psychology was focused on psychological assessment, with little attention given to treatment. This changed after the 1940s when World War II resulted in the need for a large increase in the number of trained clinicians. Since that time, two main educational models have developed—the Ph.D. science-practitioner model (focusing on research) and the Psy.D. practitioner-scholar model (focusing on clinical practice). Clinical psychologists are now considered experts in providing psychotherapy, and generally train within four primary theoretical orientations—Psychodynamic, Humanistic, Cognitive Behavioral, and Systems or Family therapy.

Clinical psychology may be confused with psychiatry, which generally has similar goals (e.g. the alleviation of mental distress), but is unique in that psychiatrists are physicians with medical degrees. As such, they tend to focus on medication-based solutions, although some also provide psychotherapeutic services as well. In practice, clinical psychologists often work in multidisciplinary teams with other professionals such as psychiatrists, occupational therapists, and social workers to bring a multimodal approach to complex patient problems.