This paper examines the interplay of professionalism, regulation, and the market in shaping accountability on the part of hospitals, physicians, and health plans. We pay particular attention to the role of accreditation. We review the development of accountability and examine its recent evolution in the context of changing information technology, consumer demands, the decline of the staff- and group-model HMO, and the reemergence of health care cost inflation. The market is emerging as the dominant influence on accountability; this development will require changes in the roles and structure of regulation, professionalism, and accreditation in assuring accountability.