Research suggests that the enhanced role of proof in mathematics classrooms presented in current standards and reform policy poses great challenges for teachers and will require substantial teacher learning. However, to date there is little research detailing what mathematical knowledge might be useful for teaching proof or how professional development might afford such learning. This paper presents a framework for Mathematical Knowledge for Teaching Proof that couples research on justification and proof in mathematics and mathematics education with Ball and colleagues' (2008) conceptualization of Mathematical Knowledge for Teaching (MKT). An empirical study of teachers' proof-related activity in professional development demonstrates the utility of this framework and provides further insights into mathematical knowledge for teaching proof. [For the complete proceedings, see ED585874.]