In recent years there has been a significant expansion in the use of provider performance measures for quality improvement, payment, and public reporting. Using data from a survey of health plans, we characterize the use of such performance measures by private payers. We also compare the use of these measures among selected private and public programs. We studied twenty-three health plans with 121 million commercial enrollees-66 percent of the national commercial enrollment. The health plans reported using 546 distinct performance measures. There was much variation in the use of performance measures in both private and public payment and care delivery programs, despite common areas of focus that included cardiovascular conditions, diabetes, and preventive services. We conclude that policy makers and stakeholders who seek less variability in the use of performance measures to increase consistency should balance this goal with the need for flexibility to meet the needs of specific populations and promote innovation. D uring the past two decades there has been substantial growth in the availability and use of performance measures. The National Quality Forum, a nonprofit organization that establishes consensus standards for measuring performance, has endorsed more than 700 measures.1 The use of provider performance measures for quality improvement, payfor-performance, and public reporting purposes has become commonplace.Performance measures increasingly play an integral role in assessing the achievement of high-quality, efficient care in new health plan and Medicare payment and delivery models such as accountable care organizations, patient-centered medical homes, and bundled and global payment.2,3 Understanding performance measures and their use is vital to ensuring the availability of reliable performance information. 4 Information on measures that are used to assess providers' performance in Medicare is publicly available through the federal rule-making process. In contrast, we are aware of only a few reports that examine the use of performance measures in the private sector. The primary focus of these reports has been the use of measures endorsed by the National Quality Forum across a cross section of users, including community collaboratives, accrediting organizations, a few health plans, and the public sector.1,5 The National Quality Forum also has catalogued the performance measures used by the Aligning Forces for Quality communities. This existing body of work provides only a limited understanding of the measures used by health plans to assess providers' performance. Consequently, little is known about how performance measures used by health plans compare with those used in public-and other privatesector programs.To address this gap in knowledge, we conducted a study with the primary purpose of gaining a better understanding of health plans'