Medical psychology has historically been defined as the branch of psychology concerned with the application of psychological principles to the practice of medicine. Medical psychology shares with the fields of health psychology and behavioral medicine an interest in the ways in which biological, psychological, and social factors interact to influence health. Medical psychologists use psychological theories and principles in order to improve the health and well-being of patients with physical illness. They are clinical psychologists who work in hospitals, medical centers, and health care facilities. Medical psychologists use techniques of psychotherapy, behavior modification, and cognitive, interpersonal, and family therapy to help patients manage chronic illness, reduce physical symptoms of disease or treatment, and manage emotional aspects of their illness.