Teamlets – dyads consisting of a physician and staff member who consistently work together – may pro- vide a simple, efficient way to reorganize primary care to create higher quality and improve patient, phy- sician, and staff experience. But little funding or policy attention has been given to teamlets;; there is no quantitative evidence on their prevalence and characteristics and no large scale study of their relation- ship to the quality and cost of care. The long-term goal of this project is to help improve primary care by discovering, evaluating, and disseminating information on high-performing primary care models. The key objectives of this mixed methods project are to assess the prevalence and characteristics of primary care teamlets in the U.S., to determine the relationship between care delivery by a teamlet and the quality and cost of care and physician burnout, and to identify the configurations – the cluster or clusters of charac- teristics – typical of high-performing teamlets. The central hypotheses are (1) the quality of care is higher and total spending on care is lower for Medicare beneficiaries who are patients of primary care teamlets;; (2) burnout is less likely in physicians who work in teamlets;; (3) teamlet performance increases with the number of years that the teamlet has worked together – at least up to a certain number of years and (4) that certain configurations of characteristics differentiate high-performing teamlets. The specific aims are (1) to determine the prevalence and characteristics of primary care teamlets in the U.S.;; (2) determine the relationship of primary care teamlets to the quality and cost of care and to physician burnout, and (3) identify the configurations of characteristics of high-performing primary care teamlets. Methodologically, the project will (1) survey a large random national sample of primary care physicians to determine the prevalence of teamlets, their characteristics, the predictors of physician participation in a teamlet, and the relationship of teamlets to physician burnout;; (2) link the survey to Medicare claims data to compare the performance of physicians in teamlets to physicians not in teamlets for important outcomes of care;; (3) interview a stratified random sample of teamlets to provide depth of understanding of teamlets and of barriers to their creation and success;; and (4) use an innovative method – Qualitative Comparative Anal- ysis – to determine the configurations of characteristics that appear to be necessary and/or sufficient for a teamlet to be high-performing. The project will provide the first large scale, critical evidence on whether primary care teamlets improve care, on the characteristics of high-performing teamlets, and on barriers to and facilitators of creating effective teamlets...