Irritable bowel syndrome (IBS) is a common, chronic functional gastrointestinal disorder affecting the large intestine, and pres-ents as abdominal pain and/or discomfort, bloating, gas retention, diarrhea, and constipation. IBS impairs quality-of-life and re-quires long-term management. In 2016, the Rome Foundation introduced new IBS diagnostic criteria (the Rome IV criteria), and al-so revised the diagnostic algorithms for, and the multidimensional clinical profile (MDCP) of, functional gastrointestinal disorders. The IBS MDCP includes clinical data, the extent to which normal daily activities are affected, and psychosocial and physiological measures. The criteria seek to aid physicians in choosing appropriate treatment for IBS patients. Herein, we seek to provide evi-dence-based practical information on IBS and functional diarrhea. We review the new Rome diagnostic IV criteria, the MDCP, and the various IBS treatment options. We suggest that, in clinical practice, combination therapies may be useful to treat patients with IBS of various grades. (Korean J Med 2017;92:366-371)