In this review essay we critically examine issues raised by authors whose work is published in the two Special Issues of "JMTE" (Part 1, 13.5 and Part 2, 13.6) on Mathematics Teacher and Mathematics Teacher Educator Change--Insight through Theoretical Perspectives. While the authors have drawn on a wide range of theories and approaches, we have chosen to view their articles through a single socio-cultural lens to explore responses to the two questions that motivated these Special Issues: (1) How are opportunities created for teachers to change themselves? (2) What do (university-based) researchers learn from working with teachers?