The relationship between mind and body and its importance to health has been recognized for thousands of years by all major healing traditions, including the ancient Greek system that gave rise to modern Western medicine. With the ascendancy in the West of the scientific method and the biomedical model of illness, however, the relationship between mind and body has often been neglected. In the 19th century, interest in hypnosis began, and later Freud championed the theory of the unconscious mind, which helped establish the paradigm that processes of the mind profoundly affect health. In the early 20th century, the American physiologist Walter Cannon began exploring the physiologic effects of emotional stimuli. In the 1930s, Dr. Clark Hull began studies of hypnosis, and research into hypnosis greatly expanded in the 1950s. The first biofeedback experiments also occurred in the 1950s. In the 1970s, Dr. Herbert Benson coined the term “relaxation response,” describing the counter-stress physiology common to many mind-body medicine practices. Since then, there has been considerable research evaluating the clinical effects of mind-body medicine. Emotions such as anger, anxiety, and depression can affect clinical outcomes (including mortality) for conditions such as cardiovascular disease, cancer, and HIV infection. The field of psychoneuroimmunology has documented, at the physiologic level, the powerful effect of the mind on the nervous, endocrine, and immune systems, and vice versa. In addition, studies have demonstrated that mind-body medicine, in addition to affecting health, can affect brain function and even structure, leading to a reevaluation of previously held beliefs about neuroplasticity.