This report presents the conceptual foundations of the OECD Programme for International Student Assessment (PISA), now in its seventh cycle of comprehensive and rigorous international surveys of student knowledge, skills and well-being. Like previous cycles, the 2018 assessment covered reading, mathematics and science, with the major focus this cycle on reading literacy, plus an evaluation of students' global competence -- their ability to understand and appreciate the perspectives and world views of others. Financial literacy was also offered as an optional assessment. The framework also includes the questionnaires distributed to students and school principals used to elicit information about student backgrounds and the school learning environment, as well as some questionnaires distributed to parents and teachers to assess factors associated with student outcomes. Students in some countries also completed further questionnaires on their educational trajectory, familiarity with information and communications technology, and well-being.