The impending arrival en masse of biosimilars on Western markets is placing drug regulatory agencies under pressure to realign their policies. Biosimilars require more rigorous assessments than traditional chemical generics. This is because of the molecular complexity of recombinant proteins, and the complexity of biological manufacturing processes. Small differences can arise in a recombinant protein product which are hard or impossible to detect with even state-of-the-art analytical techniques. Yet, these differences can have significant impact on the safety and efficacy of the drug. The European Medicines Agency (EMEA) has taken the lead in issuing guidelines, most of which are still under review. The guidelines advocate pre-clinical and clinical testing of biosimilars prior to market authorization, complemented by tailored pharmacovigilance plans. These guidelines provide a valuable base from which to develop in this evolving regulatory environment.