Any effort to integrate problem-posing instruction in school mathematics must attend to teachers' beliefs about the advantages of teaching through problem posing and especially their beliefs about the challenges of teaching in this way. This study investigated teachers who were learning how to teach mathematics through problem posing. The primary foci were the teachers' beliefs about teaching through problem posing and their problem-posing performance. The findings demonstrate that the participating teachers were able to engage successfully in problem-posing tasks and that they held a number of different beliefs about the advantages and challenges of teaching through problem posing. After participating in three workshops, a sample of teachers showed gains in problem-posing performance and in the scope and specificity of their beliefs about teaching through problem posing.