The mission of emergency medical services is to respond to unscheduled emergencies of varying severity, using resources that are limited in comparison with the diagnostic and therapeutic arsenal available within hospitals. The role of the medical dispatcher, sometimes faced with life-threatening emergencies, is crucial in the initial presumption of diagnosis, enabling the most appropriate discharge from the mobile emergency and resuscitation services (SMUR). In this book, we analyze the relationship between the diagnostic suspicions of the medical dispatcher and the intervention, through a study of clinical performance indicators.