Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders. The prevalence rate is 10-20% and women have a higher prevalence. IBS adversely affects quality of life and is associated with health care use and costs. IBS comprises a group of functional bowel disorders in which abdominal discomfort or pain is associated with defecation or a change in bowel habit, and with features of disordered defecation. The consensus definition and criteria for IBS have been formalized in the “Rome II criteria”. Food, psychiatric disorders, and gastroenteritis are risk factors for developing IBS. The mechanism in IBS involves biopsychosocial disorders; psychosocial factors, altered motility, and heightened sensory function. Brain-gut interaction is the most important in understanding the pathophysiology of IBS. Effective management requires an effective physician-patient relationship. Dietary treatment, lifestyle therapy, behavioral therapy, and pharmacologic therapy play a major role in treating IBS. Calcium polycarbophil can benefit IBS patients with constipation or alternating diarrhea and constipation.