Measuring regulatory performance is challenging, starting with defining what to measure, dealing with confounding factors, attributing outcomes to interventions and coping with the lack of data and information. This chapter describes the methodology developed by the OECD to help regulators address these challenges through a Performance Assessment Framework for Economic Regulators (PAFER), which informs this review. The chapter first presents some of the work conducted by the OECD on measuring regulatory performance. It then describes the key features of the PAFER and presents a typology of performance indicators to measure input, process, output and outcome. It finally provides an overview of the approach and practical steps undertaken for developing this review.