Mass Casualty Events (MCE) have an extraordinary impact on an entire community. The impact on victims' families, survivors, and community members is often the subject of significant attention; however, rarely does the impact on first responders (law enforcement officers, firefighters, dispatchers, crime scene investigators/photographers, etc.) garner the same coverage. Additionally, agencies can quickly become overwhelmed by the magnitude of the response causing them to overlook the psychological impact of these incidents on their personnel. Serving as specialists in police and public safety psychology, crisis intervention, and trauma recovery, the authors reflect on lessons learned from their response to multiple MCEs, including the 1999 Columbine High School shooting and the 2012 Aurora Century 16 Theater shooting, and offer recommendations to agencies regarding crisis response and trauma recovery.