EDs and emergency physicians play a critical role in health care delivery--providing care to those with life-threatening conditions, as well as serving as provider of last resort to those without options for primary care. This diversity of functions provides unique opportunities for identifying important unmet community needs and developing solutions to address these needs. Future challenges for emergency medicine include assessing and improving the quality of care provided within the ED and identifying the role of the ED in systems of care. Health services research can help define the optimal functions of emergency medicine in enhancing population health.