Recent research in mathematics education has highlighted the importance of teachers' abilities to professionally notice students' thinking. This study examined what preservice teachers professionally notice during lesson study to further describe their attention to students' mathematical thinking, their interpretations about students' reasoning, and the resulting decisions they make. Findings indicate preservice teachers commonly provided evaluative comments but were able to engage in some instances of more advanced Noticing in which they detailed students' strategies and analyzed evidence of student thinking to formulate interpretations about mathematical thinking. Analysis of these findings resulted in a framework for analyzing the content of focused and extended professional Noticing.