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Sterility assurance draws on several complementary approaches. Biological indicators use resistant, standardized spores to provide direct evidence of microbial inactivation; the appropriate organism depends on the sterilization method. Chemical indicators show whether specified process parameters were reached, while physical monitors record cycle conditions. Neither replaces the other. The Bowie–Dick test evaluates vacuum efficiency in dynamic-air-removal autoclaves, and a process challenge device places indicators in a difficult-to-sterilize configuration. Pharmaceutical sterility testing uses membrane filtration or direct inoculation into designated culture media, with incubation and controls to help assess test validity. Together, these methods support monitoring, validation, and investigation when results indicate a problem.