Performance measurement is now a key management tool used by government to assess and enhance public services. It is also used as a tool for public sector transparency and accountability. Despite these noble objectives, performance measurement can also generate counterproductive and sometimes paradoxical outcomes. This book innovatively conceptualises performance measurement as a 'policy instrument'. Such an approach necessarily invites careful and critical examination of instances of the formation, application and contestation of particular performance measurement regimes, the tools used to measure performance, the way in which performance data is produced and used, and the complex dynamics between professionals, managers and service users that arise from these practices. The book provides detailed empirical examples of performance measurement in the delivery of health, schooling and child welfare services, as well as the problematics of assessing national wellbeing. Instead of a form of scientific and rational management, performance measurement is revealed as an intrinsically contested, socio-politically charged and value laden practice. The book concludes that to succeed in delivering authentic performance improvements public sector managers must be aware of these complex, paradoxical dynamics and the circumstances that make performance measurement perform. This book was originally published as a special issue of Policy Studies.