The Primary Care Information Project (PCIP) is the largest community-based EHR project in the country and was founded in 2005. PCIP is a Bureau of the New York City Department of Health and Mental Hygiene that seeks to improve the delivery of preventive care and population health in low-income neighborhoods through the use of health IT. This report looks at the experience of PCIP in extending prevention-oriented EHRs to more than 2,500 New York City primary care providers working in medically underserved settings. Collectively, these health care settings serve upwards of two million patients, about one quarter of the total New York City population. It describes the activities of PCIP to illustrate the use of EHRs for improving public health and also discusses difficulties encountered by program staff, describes solutions, and suggests that additional support is needed to promote the widespread use of EHRs to achieve data-driven improvements in community health.