The IEA Teacher Education and Development Study in Mathematics (TEDS-M) is the first large-scale international study of the preparation of primary and lower-secondary teachers. The study investigated the pedagogical and subject-specific knowledge that future primary and lower secondary school teachers acquire during their mathematics teacher education. It also examined variations in teacher education programs within and across countries. Seventeen countries participated in TEDS-M: Botswana, Canada (four provinces), Chile, Chinese Taipei, Georgia, Germany, Malaysia, Norway, Oman (secondary teacher education), the Philippines, Poland, the Russian Federation, Singapore, Spain (primary teacher education), Switzerland (German-speaking cantons), Thailand, and the United States of America (public institutions, concurrent and consecutive routes only). This TEDS-M encyclopedia contains a chapter for each of the 17 countries in the study. The encyclopedia presents a broader context within which the data collected from future teachers and their educators can be understood and interpreted. Elements of this context include information about countries’ distinctive political, historical, and cultural contexts that influence policy and practice in mathematics teacher education. It also describes the organization and characteristics of teacher education in the participating countries, the institutions that teach future teachers and their staff, the programs and required field experiences, and the quality-assurance arrangements.