Nearly every special event or mass gathering of sufficient size to warrant dedicated medical services will likely have opportunities to interface with other agencies and organizations providing support services. In general, the larger or more complex the event, the more agencies will be involved. Law enforcement, most often local, is almost always involved in the planning and operations of a special event. Other public safety agencies such as local or mutual aid emergency medical services (EMS), the fire service, and emergency management are also commonly involved. It is important that event medical planners and leaders also interface with local and regional hospitals, including those providing specialty services for important time-critical problems (e.g., trauma, cardiac, stroke, etc.). When event venues are in rural areas, more distant from hospitals, including the area helicopter EMS provider(s) in planning is important, and often neglected. There are a number of other local, state, federal, and private organizations that may be involved in event planning and operations. This chapter is intended to provide an overview of many of these important partners that help to assure the event has sufficient resources to provide safety and security to all.