The Minimum Data Set (MDS) is a uniform instrument used in nursing homes to assess residents. In January 2008, the Centers for Medicare and Medicaid Services published a draft of a new MDS--version 3.0. This article traces the instrument's development and the design decisions that shaped it, discusses the MDS's manifest functions--data collection intended to drive quality improvement and the unintended consequences of its use--paper compliance and diminished attention to resident quality of life, and examines the revised version to gauge its success in meeting the instrument's objectives. Although results of the national evaluation of MDS 3.0 are promising, the revisions, especially those pertaining to quality-of-life assessment and the use of resident interviews and standardized assessment procedures, raise questions for future consideration. Additionally, past research suggests that the MDS's impact on quality-of-care improvement will be limited unless efforts are directed toward resolving the industry's persistent struggles with staffing, survey effectiveness, and the development of feasible care processes. MDS 3.0 seems most likely to achieve its potential if it operates within a multifaceted quality improvement framework.