\input zb-basic \input zb-matheduc \iteman{ZMATH 2013a.00129} \itemau{Novotn\'a, Jarmila; Margolinas, Claire; Sarrazy, Bernard} \itemti{Developing mathematics educators.} \itemso{Clements, M. A. (ed.) et al., Third international handbook of mathematics education. Berlin: Springer (ISBN 978-1-4614-4683-5/hbk; 978-1-4614-4684-2/ebook). Springer International Handbooks of Education 27, 431-457 (2013).} \itemab Summary: This chapter addresses, from various perspectives, issues associated with teacher education and its development. Several categories of mathematics educators are characterized and their development and roles in the teaching/learning processes are summarized. Cooperation between teachers and researchers as well as the concept of teachers as researchers are discussed from different points of view. The crucial role that observations play at all levels is analyzed and illustrated by two different models of implementation of observations into teachers' and researchers' practice. Throughout the chapter the influence of the research of Guy Brousseau on mathematics education research is recognized. \itemrv{~} \itemcc{B50 D20 C70} \itemut{teacher education; teaching-learning process; knowledge development of mathematics educators; researchers in mathematics education; mathematics educators; theories in mathematics education} \itemli{doi:10.1007/978-1-4614-4684-2\_14} \end