This introductory paper first reflects the genesis of research in mathematics and science teacher education. The analyses show a movement from foci of research in mathematics and science education from students to teachers, and then to teacher educators. Next, an overview of research in mathematics and science teacher education and its development is provided, including teacher educators’ growth. This is followed by a comparative look at the seven papers in this special issue through three lenses, focusing on who the teacher educators in these papers are, the practices which are the focus for development, and the contexts in which the professional growth is situated. The seven papers not only exemplify how teacher educators might critically and systematically reflect on their own growth, educate new teacher educators, and do corresponding research, but also demonstrate the considerable progress the research community has made with respect to the professional growth of mathematics and science teacher educators in the last decade. Finally, challenges and questions are raised, in particular in relation to raising the quality and quantity of proficient teacher educators in order to strengthen teacher education research, and to have enough human resources to offer more and better professional development opportunities and to support schools.