Biofeedback is a technique that enables an individual to learn how to change physiological activity for the purposes of improving health and performance. Biofeedback instruments are used to feed back information about physiological processes, assisting the individual to increase awareness of these processes and to gain voluntary control over body and mind. Biofeedback instruments measure muscle activity, skin temperature, electrodermal activity (sweat gland activity), respiration, heart rate, heart rate variability, blood pressure, brain electrical activity, and blood flow. Research shows that biofeedback, alone and in combination with other behavioral therapies, is effective for treating a variety of medical and psychological disorders, ranging from headache to hypertension to temporomandibular to attentional disorders. The present publication surveys these applications and reviews relevant outcome research. Biofeedback is used by physicians, nurses, psychologists, counselors, physical therapists, occupational therapists, and others.Published by Association for Applied Psychophysiology and Biofeedback.