In 1993, the World Trade Center was attacked with a vehicle-borne explosive. In 1995, the Alfred P. Murrah Federal Building Oklahoma City was bombed, and terrorists attacked the Tokyo subway with Sarin gas. To respond to these types of threats, the federal government developed the Metropolitan Medical Response System in 1997. The concept provided funding and planning framework to advance the all hazards approach to large scale incidents, with a particular emphasis on mass casualty response. The system included fire, emergency medical services, law enforcement, and public health. Both Montgomery and Prince George’s Counties in Maryland created local instances of MMRS in 2005. Over several years, in both counties, numerous multidisciplinary plans were developed to guide a cohesive response to large scale terrorist and mass casualty incidents. Nonetheless, most of these plans were jurisdiction-specific, and did not involve all relevant partners.