With an increased number of active shooter events in the United States, emergency departments are challenged to ensure preparedness for these low frequency but high stakes events. Engagement of all emergency department personnel can be very challenging due to a variety of barriers. This article describes the use of an in situ simulation training model as a component of active shooter education in one emergency department. The educational tool was intentionally developed to be multidisciplinary in planning and involvement, to avoid interference with patient care and to be completed in the true footprint of the work space of the participants. Feedback from the participants was overwhelmingly positive both in terms of added value and avoidance of creating secondary emotional or psychological stress. The specific barriers and methods to overcome implementation are outlined. Although the approach was used in only one department, the approach and lessons learned can be applied to other emergency departments in their planning and preparation. (Disaster Med Public Health Preparedness. 2019;13:345–352)