Recent acts of mass violence during active shooter events and other incidents in schools, churches and businesses continue to highlight the need for a multi-pronged strategy for both preparation and response. Further, first responders have themselves become the targets of violence in recent months during civil unrest. This special FireRescue1 guide outlines lessons identified from incidents that can direct fire department involvement in threat assessment, improve multi-agency through policy, training and procurement, and inform response and communications strategies on the ground.