This chapter reviews and reflects the development of the CERME thematic working group on "Diversity in mathematics education." The name of this group has been transformed and extended over the years, as a reflection of the change and expansion of the interests of its members. Thus "Teaching and Learning Mathematics in Multicultural Classrooms" at CERME 3 (proceedings published in 2004) has been progressively transformed into its present name "Diversity in mathematics education: Social, cultural and political challenges." To illustrate this development, this section summarises how the interests of the group have expanded throughout the years. The centrality of culture in the doing, thinking, learning, and teaching of mathematics has been discussed by many scholars in CERME meetings since they started. Already in the proceedings of CERME 1, before the creation of the group, we find many references that consider several aspects related to culture, from mathematics as a cultural product (Arzarello, Dorier, Hefendehl-Hebeker, & Turnau, 1999), to mathematical learning as being co-constructed by culture, and to the culture of mathematical classrooms (e.g., Krummheuer, 1999). Similarly, in his keynote address in CERME 1, Jeremy Kilpatrick (1999) pointed out that the increased multi-cultural and multilingual composition of many classrooms in many countries called for new research. At the next congress, CERME 2, the challenges associated with multicultural, multi-ethnic, multilingual aspects of mathematics education were addressed in several papers, for example Krummheuer (2002) who discussed the challenges in relation to both theory and methods. Bishop, Clarkson, FitzSimons, and Seah (2002) also contributed to the discussion stressing the importance of values at personal, institutional, social, and cultural levels stating that "at the cultural level, the very sources of knowledge, beliefs, and language, influence our values in mathematics education. Further, different cultures develop different values" (p. 370). Around the same time, the sudden increase in