Irritable bowel syndrome (IBS) is the most prevalent and the best studied functional gastrointestinal disorder. The etiology and the pathogenesis of IBS are still not clear; however, recent studies have implicated a role for alterations in the intestinal microbiota (dysbiosis) in the pathophysiology of the disorder. Epidemiological observations have demonstrated that the development of IBS symptoms is often preceded by a disruption of the individual's normal intestinal microbiota, and microbiological studies have demonstrated compositional differences in the intestinal microbiota between patients with IBS patients and healthy controls. In addition, animal studies and a few recent human clinical studies have demonstrated that compositional changes in the intestinal microbiota in IBS are associated with relevant abnormal gastrointestinal and brain-gut axis functions that are often observed in patients with IBS. This article discusses points of interest from the current research on the microbiota-gut-brain interactions in IBS and highlights the relevance of the emerging data to our understanding of the disorder and the clinical implications for patients' care.