EMS physicians and medical directors are often called upon to play a variety of roles before, during, and after multiple casualty incidents and mass casualty incidents. These roles can vary tremendously between EMS systems, but when appropriately utilized, an EMS physician can be an invaluable asset in terms of planning for and responding to mass casualty incidents. This chapter seeks to assemble best practices to provide a template for EMS physician roles in planning, responding to, and learning from mass casualty incidents for improved future responses. The primary focus is on the medical director's involvement in EMS system preparedness and disaster mitigation, with strategies to develop a local infrastructure of partnerships, communications, protocols, and quality improvement processes. Throughout response and recovery, the EMS medical director should focus on facilitating patient flow through effective triage and function as a liaison between the EMS system's unified command and the surrounding health care community. Counterintuitively, the EMS physician resource may not be best utilized in the delivery of acute mass casualty care or command of the incident. Physicians should continuously work toward establishing and maintaining multiagency collaboration and information exchange within the EMS system before, during, and after mass casualty incidents.