Biofeedback is a scientifically based approach, which relies on an instrumentation to measure the moment-to-moment physiological activity relevant to the problems being treated. This is based on the idea that the autonomic nervous system can come under the voluntary control through the operant conditioning. Biofeedback is a process that uses instruments to detect, measure, and amplify internal physiological responses to provide the individual with a feedback of those responses. The detection of the physiological signal with an appropriate transducer is the first step. The detected signal is then amplified and converted into a form that is accessible to the external senses. Finally, the signal is fed back to the person who then uses the information in the attempts to gain voluntary control over the targeted physiological event.For several decades, only the voluntary musculoskeletal system mediated by the central nervous system was considered responsive to the instrumental learning or the operant conditioning. However, researches had demonstrated that autonomic responses were also modifiable and began to investigate the specificity and the pattern of learned visceral responses and cognitive mediating strategies for producing visceral changes. Moreover, biofeedback also may be used in modifying a normally voluntary function when the person has lost the voluntary control because of a disease or an injury. In spite of limited understanding regarding psychophysiological mechanisms, biofeedback has been widely used in the treatment of many diseases, including constipation, incontinence, urinary dysfunction, migraine, and stress.