This chapter discusses how to measure research and experimental development (R&D) activity, noting that is highly concentrated, specially in the Business enterprise sector, but it is also widely spread across the economy. These characteristics give rise to measurement challenges as do the disparate uses of R&D statistics. These include the use of aggregate statistics for policy analysis, policy evaluation and target setting, the use of R&D expenditures as input to a capital stock of R&D in the System of National Accounts (SNA), and unit level analysis of R&D activity. Measurement, whether through surveys, the use of administrative data, or combinations of the two, requires a statistical infrastructure including registers of institutions, methodological support, means of linking data sets to enhance analytical capacity, and quality assurance standards. All of these are discussed, but, recognising that countries have quite different infrastructures and measurement challenges no specific formal recommendations are made. Sources are provided to support the development of statistical measurement.