Civilization and modern medicine now allow an unprecedented number of people to survive to old age. Not only has the definition of “old” evolved, but the aims of medical care for the elderly have progressed far beyond survival to maximizing functional and cognitive status, improving quality of life, and preserving productivity. Although many health problems in older age can be prevented or postponed by medical interventions, the quality of medical care for older persons remains largely unexamined. Previous work on quality-of-care measurement has focused on specific diseases or aspects of care, and in some cases targeted only a slice of the older population (1–6). Such targeted approaches may not present a fair picture of overall quality and may lead to unintended incentives (“gaming the system”) (7). Although broad systems of quality-of-care evaluation are less susceptible to “gaming,” they seldom include quality indicators focused on aspects of care important to older sick persons (8, 9). Substantial variation in preferences may make quality of care for older adults particularly difficult to measure. For example, older adults do not consistently prefer care that prolongs life, particularly if this care occurs at the expense of comfort. Furthermore, many ill, older adults cannot advocate for themselves and may have no family members or friends to do so on their behalf. Thus, objective measures of the care they receive are particularly important. The Assessing Care of Vulnerable Elders (ACOVE) project endeavored to develop a comprehensive set of quality-assessment tools for ill older persons. Because “ill older persons” constitute a heterogeneous cohort that is not easily delineated, we created a system to identify high-risk, community-dwelling individuals and targeted the most important clinical conditions affecting them. Specifically, our goals for this project were the following: 1. Develop a definition of “vulnerable elders” that delineates a group of community-living persons 65 years of age and older who are at high risk for death or functional decline, and develop a system to identify them. 2. Identify important medical conditions that affect vulnerable elders and for which effective methods of prevention or management exist. 3. Develop a set of evidence-based, quality-of-care indicators that are relevant to vulnerable elders using systematic literature reviews, expert opinion, and the guidance of expert groups and stakeholders. 4. Design a chart abstraction tool, interview instrument, and administrative data analytic methods to implement the quality-of-care indicator system.