Introduction: Irritable bowel syndrome (IBS) is a common condition in clinical practice. There are currently no objective tests to rule in the disease, but rather tests to rule out other diseases. Biomarkers in IBS may provide the tools needed for diagnosis, prognosis and therapy. These include identification of differences in microbial composition, immune activation, bile acid composition, colonic transit, and alteration in sensation in subgroups of IBS patients. Areas covered: Studies included in our review were chosen based on a PubMed search for 'biomarkers' and 'IBS'. We have reviewed the literature on biomarkers to appraise their accuracy, validity and whether they are actionable. We have not covered genetic associations as biomarkers in this review. Expert commentary: There is significant promise in the usefulness of biomarkers for IBS. The most promising actionable biomarkers are markers of changes in bile acid balance, such as elevated bile acid in the stool, and altered colonic transit. However, there is also potential for microbial studies and mucosal proteases as future actionable biomarkers.