Emergency medical services systems consist of the organizations, individuals, facilities, and equipment whose participation is required to ensure timely and medically appropriate responses to requests for prehospital care and medical transportation. The system design determines how resources are structured – operationally, financially, legally, and politically. System design affects virtually every aspect of how requests for services are handled. The design of the system should support the primary goals of providing the best clinical and service quality possible with available resources. The principles and elements of emergency medical services system design vary in some respects between environments, organizational settings, health care systems, community settings, and cultures. Because changes to the emergency medical services system design can have a profound effect on clinical outcomes, community satisfaction, and cost, it is vital for emergency medical services and community leaders to have a sound understanding of system design principles and elements.