Generic forms of chemically-derived drugs must exhibit chemical identity and be bioequivalent in healthy human subjects. The use of generic drugs results in a considerable savings of healthcare expenditures. Biologic drugs are produced in living systems or are derived from biologic material and extend beyond proteins to include antibodies, polysaccharides, polynucleotides, and live viral material. Such drugs pose a challenge to characterize as they tend to be larger in size than chemically-derived drugs, can exhibit a variety of post-translational modifications, and can have activities that are dependent on specific conformations. Biosimilars are not true generics, but rather, exhibit a high degree of similarity to the reference product and are considered to be biologically and clinically comparable to the innovator product. Therefore, the development process for biosimilars is more complex than for a true generic. Guidance is now available from the US Food and Drug Administration and from the European Medicines Agency for the development of biosimilar drugs. Biosimilar drugs are expected to have a major impact in the management of various diseases in coming years.