Biopharmaceuticals are drug products containing biotechnology-derived proteins as active substances, and have revolutionised the treatment of many diseases. A number of biopharmaceutical patents are due to expire in the next few years, or have already expired. The subsequent production of follow-on products, or 'biosimilars' has aroused interest within the pharmaceutical industry as biosimilar manufacturers strive to obtain part of an already large and rapidly-growing market. The potential opportunity for price reductions versus the originator biopharmaceuticals remains to be determined, as the advantage of a slightly cheaper price may be outweighed by the hypothetical increased risk of side-effects from biosimilar molecules that are not exact copies of their originators. This review focuses on the issues surrounding biosimilars, including manufacturing, quality control, clinical efficacy and side effects, and how government and industry regulations are evolving to deal with these topics.