Irritable bowel syndrome (IBS) is a prototype of disorders of gut–brain interaction, which is characterized by chronic abdominal pain associated with bowel movement, changes in stool consistency, and/or changes in frequency of defecation. Subtypes of IBS are identified as IBS with predominant constipation, with predominant diarrhea, with mixed bowel habits, and unclassified. Prevalence of IBS in the general population of the world/Japan is 4.1%/2.2% with dominance in females and younger age. The exact cause of IBS remains unknown. However, research suggests that environmental factors, including acting on individuals with susceptibility genes, lead to the onset of IBS. Pathophysiology of IBS is summarized as brain–gut interactions, which include abnormal stress responses, increased lower gastrointestinal motility, visceral hypersensitivity, and psychological abnormalities, such as anxiety, depression, and somatization. Gut microbiota abnormalities, increased mucosal permeability, and mucosal microinflammation are upstream factors. Diagnosis is based on the Rome IV criteria, which will be updated to the Rome V criteria. Clinical practice guidelines recommend a step-wise approach. The initial step is gut-targeted therapy with behavioral modification, including diet and exercise, probiotics, polycarbophil, and visceral neuromodulators. The second step is neuropharmacological treatment using central neuromodulators. The third step is brain–gut behavioral therapies. Further advancement of the clinical practice of IBS is warranted.