Despite 3 decades of scientific progress, rates of survival from out-of-hospital cardiac arrest remain low. The Cardiac Arrest Registry to Enhance Survival (CARES) was created to provide communities with a means to identify cases of out-of-hospital cardiac arrest, measure how well emergency medical services (EMS) perform key elements of emergency cardiac care, and determine outcomes through hospital discharge. CARES collects data from 3 sources-911 dispatch, EMS, and receiving hospitals-and links them to form a single record. Once data entry is completed, individual identifiers are stripped from the record. The anonymity of CARES records allows participating agencies and institutions to compile cases without informed consent. CARES generates standard reports that can be used to characterize the local epidemiology of cardiac arrest and help managers determine how well EMS is delivering out-of-hospital cardiac arrest care. After pilot implementation in Atlanta, GA, and subsequent expansion to 7 surrounding counties, CARES was implemented in 22 US cities with a combined population of 14 million people. Additional cities are interested in joining the registry. CARES currently contains more than 13,000 cases and is growing rapidly.