The TIMSS 2015 Encyclopedia: Education Policy and Curriculum in Mathematics and Science is a valuable compendium of how mathematics and science are taught around the world. Each TIMSS 2015 country and benchmarking participant completed the TIMSS 2015 Curriculum Questionnaire and prepared a chapter summarizing key aspects of mathematics and science education. The chapters describe the structure of each education system, the mathematics and science curricula in the primary and lower secondary grades, and overall policies related to mathematics and science instruction (e.g., teacher education, instructional materials, and assessment). The chapters were prepared from each country’s viewpoint, written primarily by experts from ministries of education, research institutes, or institutions of higher education with extensive knowledge about their country’s education system. Taken together, the data from the curriculum questionnaire and the information in the chapters present a concise yet rich portrait of mathematics and science curricula and instruction around the world, and make the TIMSS 2015 Encyclopedia an indispensable resource for policy and research in comparative education.