This chapter considers the politics of data, how data and datafication are defined, and then attempts to map out the existing research on data and education internationally. Data in education are integral to a particular political understanding of what matters in education, based on neoliberal values of competition. The problems associated with the use of data in education can be broadly grouped into two categories: those related to effectiveness and those related to identities. The idea of using simple progress measures is established in the education system, but more complex calculations have been used with more caution. The introduction of Baseline Assessment in 2015 marked the epitome of a trend towards using 'simple progress' as a key judgement on a school's quality. The chapter further examines the current policy context of primary and early years education in England, with the aim of providing the background for the research data. It presents an overview of some concepts discussed in this book.