National and regional data aggregation and reporting efforts are each important in their own right, and together have had a huge impact on the quality of care delivered across the United States. AF4Q Alliances have created regional data sets, collecting clinical and claims data from multiple payers, including a majority of providers and systems within a given Alliance's region, and aggregating those data to measure health care quality and outcomes. The collective experience of the 16 Alliances working to develop and use data sets for public reporting, quality improvement, payment reform, and benefit design offers valuable lessons about how regional and national measurement efforts can play complementary roles to improve quality and value.