Description:IBS is a functional bowel disorder characterized by symptoms of abdominal pain or discomfort and associated with disturbed defecation. The syndrome is understood in terms of multiple physiological determinants contributing to a common set of symptoms rather than as a single disease entity. Current and future diagnostic approaches and treatments will depend on identifying the specific pathophysiological subgroups contributing to these symptoms. This issue is devoted to the diagnosis, treatment, and managment of this disorder.