Irritable bowel syndrome is a biopsychosocial disorder that results from dysregulation of central and enteric nervous system function. It manifests as dysmotility and/or visceral hypersensitivity, and is modified by psychosocial processes. The interaction of the biopsychosocial factors determines the experience of the illness. An understanding of the biopsychosocial model of illness requires a shift from concepts traditionally taught in Western medical schools (biomedical reductionism and dualism) to that of multicausality, where biologic and psychologic factors interact to determine the disease and its experience or illness.