The safety of biological products (biologics) derived from in vitro cultured cell lines of animal origin is dependent both on clinical studies to evaluate efficacy, and a matrix of controls throughout the manufacturing process to assure consistency, quality, and safety of the marketed product for human use. One major area of concern is virus safety. Through the combination of: (A) careful selection of raw materials; (B) testing of process intermediates; and (C) virus clearance evaluations of the individual steps in the manufacturing process; biologics manufacturers can demonstrate that their products are free from detectable adventitious and endogenous viruses. Comprehensive regulatory guidance suggests approaches for virus testing of biologics at early and later stages of clinical development and, although some countries have specific requirements, many of these approaches are harmonized worldwide. In general, regulatory authorities expect purification processes to include multiple steps with complementary, or orthogonal, methods for virus reduction including inactivation and separation or removal. Each step in the process may be more or less effective for reducing levels of different test viruses, and therefore selection of the appropriate panel of test viruses for the specific product is critical for viral clearance studies…