While technology has potential to improve the teaching and learning of mathematics, research indicates that teachers struggle in their efforts to implement technology-rich mathematical tasks in their classrooms. Effective technology integration in mathematics requires teachers to be able to apply their classroom knowledge related to mathematics content, pedagogies, educational technologies and the interplay between those aspects of knowledge. In recent years, Technological and Pedagogical Content Knowledge (TPACK) has emerged as a construct to describe teachers' knowledge related to effectively integrating technology. In this paper, we use the framework to consider how professional development programs can develop teachers' TPACK through the exploration of technology-rich mathematical tasks. (Contains 1 note, 2 tables, and 2 figures.)