This review examines past, current, and future issues in developing and using public health performance data for improving the public health system. Issues are explored relating to public health performance data collection and analysis, and inferences made from those data, largely by examining public health performance data collected since the Year 2000. More research is needed to improve understanding of the context in which public health systems operate and how that context affects performance and its relationship to health outcomes. There are major areas of concern that must be addressed by the public health practice organizations, governmental public health entities, and the public health systems research communities, such as ensuring that data are collected on public health infrastructure, practice, and performance and that data from various sources are collected in a harmonious fashion. At issue also is the examination of the impact of new arrivals to the public health system, such as accreditation and credentialing of the public health workforce, on public health system performance.