This chapter aims to explore my experiences within the context of transitioning from mathematics teaching to mathematics teacher education. My experiences as a mathematics teacher have prompted me to reflect on various aspects of the process of developing expertise as a mathematics teacher educator (MTE). Utilising reflection in this transition process, I use self-study as a methodological approach. Self-study enables individuals to participate in reflective practices, conduct in-depth evaluations of teaching activities, and develop hypotheses about the learning process. The findings suggest that self-study has helped to reveal my personal pedagogy and enhance my awareness of how I am developing expertise as a MTE. This chapter offers insights into the role of reflection in the transition from mathematics teacher to MTE.