The Programme for International Student Assessment (PISA) is a worldwide research project involving schools and students in over 70 countries. It is run by the Organisation for Economic Co-operation and Development (OECD), takes place every three years, and is designed to examine how 15-year-olds can apply what they have learned in school to real life situations. This briefing provides an introduction to PISA 2015; its key findings in England, Northern Ireland, Scotland and Wales; and background information on social context and the education systems of the four nations.