The U.S. health care system is struggling to improve the quality of health care while containing costs. The rapidly expanding population of older adults with serious illness presents both the greatest challenge and potentially the greatest opportunity to achieving this goal. In order to capitalize on this opportunity, we must first examine the epidemiology of the care of older adults with serious illness, that is, a full description of the characteristics and quality of care from the time of diagnosis through the full course of illness, including measurement of all factors that may influence or impact that care. Several methodological challenges exist in this area of study, including but not limited to, defining the onset of serious illness, avoiding bias in sample selection, and measuring the full breadth of personal, social, local, regional and provider factors that may influence care. Yet, this work is possible through a combination of targeted primary research and efficient leveraging of ongoing studies and existing data sources. Through these studies, we may identify those factors and services associated with high value health care, and learn to develop and refine policies and health care delivery models that yield the greatest improvements in care for seriously ill older patients and their families.