The field is often considered to have begun in 1896 with the opening of the first psychological clinic at the University of Pennsylvaniaby LightnerWitmer. 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. scientist–practitioner model (requiring a doctoral dissertation and extensive research experience in addition to clinical expertise) and, in the U.S. the Psy.D. practitioner–scholar model (requiring completion of either a dissertation or other doctoral project, with extensive focus on clinical expertise in addition to research). While training programs using either model, if accredited by the American Psychological Association, are required to teach the full spectrum of psychological science, including both research and clinical practice, the primary objective of Ph.D. programs has historically been training students in conducting research as well as clinical practice; while the primary objective of Psy.D. programs has been preparing students to apply their knowledge in clinical practice.
Clinical psychologists provide psychotherapy, psychological testing, and diagnosis of mental illness. They generally train within four primary theoretical orientations—psychodynamic, humanistic, cognitive-behavioral (CBT), and systems or family therapy. Many continue clinical training in post-doctoral programs in which they might specialize in disciplines such as psychoanalytic approaches or child and adolescent treatment modalities.