Background?Although the value of clinical registries has been well recognized in developed countries, their use for measuring the quality of emergency medical service care remains relatively unknown. We report the methodology and findings of a statewide emergency medical service surveillance initiative, which is used to measure the quality of systems of care for patients with out-of-hospital cardiac arrest. Methods and Results?Between July 1, 2002, and June 30, 2012, data for adult out-of-hospital cardiac arrest cases of presumed cardiac cause occurring in the Australian Southeastern state of Victoria were extracted from the Victorian Ambulance Cardiac Arrest Registry. Regional and temporal trends in bystander cardiopulmonary resuscitation, event survival, and survival to hospital discharge were analyzed using logistic regression and multilevel modeling. A total of 32?097 out-of-hospital cardiac arrest cases were identified, of whom 14?083 (43.9 ) received treatment by the emergency medical service. The risk-adjusted odds of receiving bystander cardiopulmonary resuscitation (odds ratio [OR], 2.96; 95 confidence interval, 2.62?3.33), event survival (OR, 1.55; 95 confidence interval, 1.30?1.85), and survival to hospital discharge (OR, 2.81; 95 confidence interval, 2.07?3.82) were significantly improved by 2011 to 2012 compared with baseline. Significant variation in rates of bystander cardiopulmonary resuscitation and survival were observed across regions, with arrests in rural regions less likely to survive to hospital discharge. The median OR for interhospital variability in survival to hospital discharge outcome was 70 (median OR, 1.70). Conclusions?Between 2002 and 2012, there have been significant improvements in bystander cardiopulmonary resuscitation and survival outcome for out-of-hospital cardiac arrest patients in Victoria, Australia. However, regional survival disparities and interhospital variability in outcomes pose significant challenges for future improvements in care.