For problem posing to be implemented in mathematics classrooms, preservice teachers need to learn how to teach mathematics through problem posing. In this chapter, I summarize and reflect on research in mathematics teacher education programs that took place while preservice teachers were studying mathematics teaching practice. In the problem-posing experiences presented here, the focus is on creating new problems and reformulating given problems. Although these training programs are diverse, they share the common goal of understanding the types of problems that preservice teachers will consider using in their mathematics classes and encouraging them to be problem creators together with their students.