Recent improvised explosive device (IED) and active shooter incidents reveal that some traditional practices of first responders need to be realigned and enhanced—with an emphasis on early hemorrhage control and a more integrated response by first responders (i.e., emergency medical services [EMS], fire, law enforcement, and rescue personnel)—to improve survivability of victims and the safety of first responders caring for them.1 At the request of first responders and first receivers (e.g., medical technicians, nurses, and physicians) who have encountered mass casualties from IEDs and/or active shooter incidents, this document was developed to provide guidance on how to better approach these incidents. Responders should also consider the combination of both IEDs and active shooter incidents in an organized, complex attack (such as the Mumbai attacks in 2008) that requires both treatment and extraction of the injured from a still-hostile environment. The conditions during such tactical assaults in a civilian setting speak to the need for first responders and first receivers to adopt evidence-based hemorrhage control, risk evaluation, and casualty management measures in a potentially dangerous environment. As a result of these developments, the Department of Homeland Security, in coordination with the Department of Defense (DoD), Department of Health and Human Services, Department of Justice, Department of Transportation, White House Office of Science and Technology Policy, and the National Security Staff, has developed recommendations for individuals who provide emergent and immediate medical management of casualties resulting from IEDs and/or active shooter incidents. Based on best practices and lessons learned, this document focuses on the medical response to IEDs and/or active shooter incidents with recommendations for hemorrhage control, protective equipment (which includes ballistic vests, helmets, and eyewear), and response and incident management.