IEA’s TIMSS 2019 is the seventh assessment cycle of TIMSS, the Trends in International Mathematics and Science Study. TIMSS 2019 was conducted at the fourth and eighth grades in 64 countries and 8 benchmarking systems. Inaugurated in 1995, TIMSS has been conducted every four years since, providing 24 years of trends in mathematics and science achievement. The TIMSS assessments of student achievement are updated with each cycle in collaboration with the participating countries, who review the frameworks describing the mathematics and science content to be assessed and participate in item development. TIMSS also provides important policy relevant data about students’ contexts for learning mathematics and science based on questionnaires completed by students and their parents or caregivers, teachers, and school principals. Taken together, TIMSS provides comparative data about countries’ student achievement over time and in relation to key home, school, and classroom variables.