Since 2001, the results of PISA (Programme for International Student Assessment) have been made public every three years. There has been increasing interest in their assessments of the current state of national educational systems. While ‘rankings’ are perhaps the most widely known outcome of PISA tests, they are not their most interesting or useful outcome. The OECD PISA study represents an unprecedented source of data that has been used and analyzed by many researchers for a number of years. The international PISA tests have also fostered critical reflection on the diversity of approaches and uses of PISA results at a national level. This overview provides an introduction to the literature on PISA results and to the uses of PISA as an instrument of educational policy-making.