This Research Forum highlights the most recent research on the development of the role of the teacher of mathematics within mathematics classrooms that involve the use of technological tools, with an emphasis on teachers’ experiences within both formal and informal professional development programmes. We foreground the theoretical ideas and methodological approaches that focus on the development of classroom practices at the levels of both individual teachers and communities of teachers, charting their respective development over time. The RF makes reference to a previous forum at PME37 on the theme of Meta-Didactical Transposition (Aldon et al.,2013a), a theoretical framework that has evolved from research in this area.