The irritable bowel syndrome (IBS) is a functional gastrointestinal disorder whose hallmark is abdominal pain or discomfort associated with a change in the consistency or frequency of stools. In the western world, 8% to 23% of adults have IBS and its socioeconomic cost is substantial. Research-generated insights have led to the understanding of IBS as a disorder of brain-gut regulation. The experience of symptoms derives from dysregulation of the bidirectional communication system between the gastrointestinal tract and the brain, mediated by neuroendocrine and immunological factors and modulated by psychosocial factors. The biopsychosocial model integrates the various physical and psychosocial factors that contribute to the patient's illness. This model and the recently revised symptom-based criteria (i.e. the "Rome II criteria") form the basis for establishing a comprehensive and effective approach for the diagnosis and management of the disorder.