Biosimilar therapeutic proteins in oncology offer the potential to decrease costs while providing safety and efficacy profiles consistent with their respective reference or originator products. Biosimilars have a number of important differences from generic small-molecule drugs, including manufacturing processes that are unique from their reference products. These differences may affect biosimilars through posttranslational modifications that can occur in specific cellular production lines, and these modifications have potential effects on protein structure, function, clinical pharmacology, and immunogenicity. Regulatory agencies expect these differences to be identified, analyzed, and minimized through iterative processes and extensive preclinical efforts. Generic naming of biosimilars reflects the nonproprietary reference product name along with a meaningless four-letter suffix to ensure that each product can be uniquely identified for prescribing and pharmacovigilance purposes. Labeling information for biosimilars reflects a greater detail of comparisons to reference products than conventional generic drugs, which ensures that prescribers can understand the source of information and have a complete understanding of the therapeutic profile of each biosimilar agent. Postmarketing surveillance programs will be required to evolve and ensure optimal pharmacovigilance reporting, because the potential for unexpected adverse events with biosimilars is higher than with conventional generic agents as a result of different manufacturing processes and different clinical trial designs and durations. The existing filgrastim biosimilars are likely to be joined soon by therapeutic monoclonal antibodies, including rituximab, trastuzumab, and bevacizumab, on the basis of patent expiration dates and clinical trial results.