Irritable bowel syndrome is one of the most commonly encountered functional gastrointestinal disorders, affecting an estimated one in five adult Americans. It is characterized by a symptom complex that includes chronic abdominal pain and discomfort that is relieved with defecation, abnormal stool frequency, and a change in stool form. Although the etiology of this disorder continues to remain elusive, this article reviews the current theory of the pathophysiologic mechanisms and reports on diagnostic and management principles for the primary care provider.