Abstract: The United States Food and Drug Administration (FDA) is the regulatory authority overseeing medical products and plays a critical role in protecting the public from chemical, biological, radiological, nuclear (CBRN) threats and emerging infectious diseases. It is responsible for reviewing the safety and efficacy of medical countermeasures (MCMs), including drugs, therapeutic biologics, vaccines, and devices; using legal mechanisms to facilitate emergency use; monitoring MCMs use for adverse events, and collaborating with government partners for preparedness and response. This article briefly introduces FDA regulations related to MCMs, emergency use and FDA preparedness and response to public health emergency.