Various stakeholders have made significant efforts to measure and improve health care quality, spurred by landmark reports issued over a decade ago that highlighted serious deficiencies. Most payers now require providers of care to report on aspects of quality as a way to measure their performance and hold them accountable for it. The most common types of initiatives to measure and improve health care quality are public reporting programs and pay-for-performance programs. Under public reporting programs, providers’ performance on quality measures is publicly disseminated to help consumers make informed choices about their care (which may also motivate providers to improve their quality). In pay-for-performance programs, providers’ quality scores directly affect their payments. Both types of initiatives use various information and financial incentives to encourage providers to follow evidence-based guidelines and processes, improve patients’ experiences when receiving care, and improve clinical outcomes. Despite the growing use of quality measures, progress has been slow, and many deficiencies in quality persist. This paper provides an overview of the current state of quality measurement, and it uses initiatives developed and implemented through the Medicare program to illustrate the key issues and challenges that arise in measuring and improving the quality of providers.