For more than 50 years, the International Association for the Evaluation of Educational Achievement (IEA) has been instrumental in developing an analytical model for understanding the relationships between educational policy (the intended curriculum), classroom and instructional practices (the implemented curriculum), and educational learning outcomes (the achieved curriculum). The "TIMSS 2011 Encyclopedia" describes the intended curriculum in the countries and sub-national jurisdictions that participated in the TIMSS 2011 assessment, providing a detailed description of the national contexts for the teaching and learning of mathematics and science. Each TIMSS 2011 participant contributed a chapter to this volume summarizing the overall structure of its education system, its mathematics and science curricula and instructional approaches at the primary and lower secondary levels, its requirements for teacher preparation, and the types of assessments and examinations that are employed to monitor educational outcomes at the national level. The policy-related information provided in the "TIMSS 2011 Encyclopedia" is intended to complement the data on educational outcomes that are provided in the companion reports, "TIMSS 2011 International Results in Mathematics" and "TIMSS 2011 International Results in Science" (ED544560). This information may be used not only to help understand the relationships among policies, practices, and outcomes within countries, but also to provide potentially powerful insights into international best practice. (Individual sections contain references, suggested readings, and/or exhibits.) [For Volume 2, see ED544562.]