Study objective: Large-scale quality and performance measurement across unaffiliated hospitals is an important strategy to drive practice change. The Michigan Emergency Department Improvement Collaborative (MEDIC), established in 2015, has baseline performance data to identify practice variation across 15 diverse emergency departments (EDs) on key emergency care quality indicators. Methods: MEDIC is a unique physician-led partnership supported by a major third-party payer. Member sites contribute electronic health record data and trained abstractors add supplementary data for eligible cases. Quality measures include computed tomography (CT) appropriateness for minor head injury, using the Canadian CT Head Rule for adults and Pediatric Emergency Care Applied Network rules for children; chest radiograph use for children with asthma, bronchiolitis, and croup; and diagnostic yield of CTs for suspected pulmonary embolism. Baseline performance was established with statistical process control charts. Results: From June 1, 2016, to October 31, 2017, the MEDIC registry contained 1,124,227 ED visits, 23.2% for children (<18 years). Overall baseline performance included the following: 40.9% of adult patients with minor head injury (N=11,857) had appropriate CTs (site range 24.3% to 58.6%), 10.3% of pediatric minor head injury cases (N=11,183) exhibited CT overuse (range 5.8% to 16.8%), 38.1% of pediatric patients with a respiratory condition (N=18,190) received a chest radiograph (range 9.0% to 62.1%), and 8.7% of pulmonary embolism CT results (N=16,205) were positive (range 7.5% to 14.3%). Conclusion: Performance varied greatly, with demonstrated opportunity for improvement. MEDIC provides a robust platform for emergency physician engagement across ED practice settings to improve care and is a model for other states.