The growth of education systems and the construction of the state have always been connected. The processes of governing education systems always utilized data through a range of administrative records, pupil testing, efficiency surveys and international projects. By the late twentieth century, quantitative data had gained enormous influence in education systems through the work of the OECD, the European Commission and national system agencies. The creation and flow of data has become a powerful governing tool in education. Comparison between pupils, costs, regions and states has grown ever more important. The visualization of this data, and its range of techniques, has changed over time, especially in its movement from an expert to a public act. Data began to be explained to a widening audience to shape its behaviours and its institutions. The use of data in education systems and the procedures by which the data are constructed has not been a major part of the study of education, nor of the histories of education systems. This volume of contributions, drawn from different times and spaces in education, will be a useful contribution to comparative historical studies.