How government activities are measured matters. The size and the economic significance of the public sector make it a major contributor to economic growth and social welfare. The goods and services government provides, its redistributive and regulatory powers, and how those are exercised affect the way business is conducted and people live their lives in every country. Citizens are entitled to understand how government works and how public revenues are used. The last two decades have been characterised by significant public management reforms in OECD countries, but these have often been driven by policy fashion rather than solid evidence about costs and impacts, and arguably with significant over-claiming about best practices. Addressing this concern, Measuring Government Activity provides a significant contribution to developing a coherent, reliable system for data collection and analysis. It summarises the available OECD and other international data on public sector inputs and processes. It also examines the existing internationally comparable data on outputs and outcomes, an area that is at present limited, and recommends new approaches to measurement. This report is a companion to the new OECD biennial Government at a Glance and will interest policy makers, civil servants and academics alike.