Since the National Council of Teachers of Mathematics ([NCTM], 2000) and the National Research Council ([NRC], 2005) revealed that problem posing needed to be incorporated into mathematics classrooms, the importance of teachers' roles in problem posing has been emphasized in K-12 mathematics curriculum because of instructors' impact on students' mathematical performance. In the present study, researchers investigated teachers' subject matter knowledge (SMK), knowledge of content and teaching (KCT), and knowledge of content and students (KCS) in terms of problem-posing. A qualitative study design and inductive analysis were used to gather and interpret data from interviews conducted with four mathematics teachers. Results indicated that participants had SMK of problem posing, but their actual problem-posing results did not reflect their SMK well. In terms of KCS and KCT, teachers were aware of the importance of problem posing for students' mathematical development but felt that there were several significant factors impeding the effective incorporation of problem posing within their classes. These findings underscore the importance of professional development for teacher pedagogical knowledge in problem posing.