Dr. Ellner also practices primary care medicine at the Phyllis Jen Center for Primary Care at Brigham and Women's Hospital. His work focuses on the redesign of health service delivery and medical training to incorporate advances in information technology, to hasten the adoption of higher functioning organizational models, and to better address the social determinants of health. He previously worked with the World Health Organization and Clinton HIV/AIDS Initiative on projects to improve health systems in low- and middle-income countries. He serves on the board of several non-profit organizations focused on advancing primary care and community health.