People receive medical care in different places based on their health insurance, where they live and other characteristics. There is, however, surprisingly little research examining whether these differences impact healthcare delivery or health outcomes. To ensure high quality healthcare for all, we must identify, quantify, and address differences in quality or outcomes that we find. This study will use retrospective ambulatory visit data for 12 million unique patients from five medical centers across New York City (NYC) to assess the level of differences among ambulatory practices by insurance and other factors, and how these differences impact processes of care and health outcomes. We will use detailed concurrent and prospective data regarding clinical configurations, processes, and policies in the Mount Sinai Health System to further characterize how multiple factors and practice characteristics operate and to evaluate the impact of current and planned changes to improve care. Our health system is undertaking a transformational set of initiatives to standardize the quality of care in ambulatory practices system-wide, creating an opportunity to observe the impact of various strategies. We will accomplish the following aims: 1) use NYC-wide data to describe the homogeneity vs heterogeneity of hospital-based and faculty practice ambulatory sites with respect to insurance and other factors and examine their association with selected quality measures of preventive care (pediatrics), procedural care (obstetrics), and chronic disease management (general and family medicine); 2) Identify differences between homogeneous vs. heterogeneous practices in a large academic medical center, their association with care quality, and with patient, staff, provider and trainee perceptions and experiences; and 3) observe effects of standardization over time on quality measures, and using microsimulation techniques, estimate the potential impact of widespread dissemination of successful strategies on selected cardiometabolic outcomes. We will use our findings to build a blueprint that other healthcare systems can follow to improve care in their ambulatory practices. The proposed study will increase our understanding of strategies to improve the quality of outpatient care in our nation and will inform institutional efforts to improve healthcare systems.