Few problems common in management reform are more prominent or more vaguely conceived than is leadership. Advocates and observers broadly agree that leadership is a critical factor where reform takes hold. Yet, in scholarship assessing the results-model management reforms proliferating in public organizations during the last decade and a half, leadership remains an elusive concept, rarely subject to empirical scrutiny. Applying the logic of credible commitment drawn from the study of institutional political economy, this article models leadership commitment as a factor shaping organizational responses to reform. Quantitative analysis of data drawn from two Government Accountability Office surveys of agency managers administered during the implementation of the Government Performance and Results Act provides evidence regarding the impact of leadership commitment on perceived credibility results-based reform and reported use of performance measures. The article concludes with a brief discussion of reputation-based credibility and the skepticism many government managers hold toward reform.