Accountability has become a major issue in health care. Accountability entails the procedures and processes by which one party justifies and takes responsibility for its activities. The concept of accountability contains three essential components: 1) the loci of accountability--health care consists of at least 11 different parties that can be held accountable or hold others accountable; 2) the domains of accountability--in health care, parties can be held accountable for as many as six activities: professional competence, legal and ethical conduct, financial performance, adequacy of access, public health promotion, and community benefit; and 3) the procedures of accountability, including formal and informal procedures for evaluating compliance with domains and for disseminating the evaluation and responses by the accountable parties. Different models of accountability stress different domains, evaluative criteria, loci, and procedures. We characterize and compare three dominant models of accountability: 1) the professional model, in which the individual physician and patient participate in shared decision making and physicians are held accountable to professional colleagues and to patients; 2) the economic model, in which the market is brought to bear in health care and accountability is mediated through consumer choice of providers; and 3) the political model, in which physicians and patients interact as citizen-members within a community and in which physicians are accountable to a governing board elected from the members of the community, such as the board of a managed care plan. We argue that no single model of accountability is appropriate to health care. Instead, we advocate a stratified model of accountability in which the professional model guides the physician-patient relationship, the political model operates within managed care plans and other integrated health delivery networks, and the economic and political models operate in the relations between managed care plans and other groups such as employers, government, and professional associations.