Biologic agents have revolutionized the care management of many life-threatening and debilitating diseases. As patents for older biologic therapies have begun to expire, the market has opened to copy versions of the originators - commonly referred to as biosimilars, follow-on biologic agents or subsequent-entry biologic agents - which are expected to gain a portion of the market, reduce health-care spending and increase treatment access worldwide. Importantly for patients with IBD, CT-P13 was the first biosimilar to infliximab that obtained regulatory approval by the European Medicines Agency in September 2013 and by the FDA in April 2016. In May 2016, SB2 was the second biosimilar to infliximab receiving marketing authorization in Europe. Currently, >20 other biosimilars to infliximab and adalimumab are in the development pipeline. Their similar-but-not-identical nature, and the concept of extrapolating efficacy and safety data from one therapeutic indication to another, seem to be confusing to physicians and cause concerns about the efficacy and safety of biosimilar products. A relevant debate is still ongoing in the field of IBD. This Review discusses the scientific principles underlying the biosimilar concept established in Europe and the USA, and discusses the current state of knowledge on biosimilar use in IBD.