Purpose: Irritable bowel syndrome (IBS) is frequently yet little understood disease. Review was performed to promote understanding on the characteristics, pathophysiology, and risk factors of IBS. Content: IBS is characterized by abdominal discomfort associated with pain and altered bowel function; structural and biochemical abnormalities are absent. Generally IBS is more prevalent in women and people with higher educational and social background, but there are some controversies. IBS is diagnosed by the Rome II or Manning criteria after excluding organic gastrointestinal diseases. The pathophysioloy is explained by abnormal control mechanism of central and enteric nervous system. Mucosal immunity, secretions, and neurotransmitter are also associated with the hypersensitivity and motility change of bowel function. Stress is known as a major triggering factor and contributed to symptoms. Other risk factors are genetic elements, childhood experiences, inflammation, anxiety, depression, diet, and sleep disorders.