Pedagogical content knowledge, the particular ways that teachers understand their subjects in order to instruct others, has been described and explored in the math and science education fields in some depth, yet little research exists illustrating this concept in music instruction. I used a descriptive approach to explore expert beginning band teachers' thinking as they viewed videotaped performances of sixth-grade instrumental music students in their first year of instruction. I categorized the expert teachers' comments using models of pedagogical content knowledge from previous research in other subject areas in order to understand how music teachers use these skills. Teachers in the study each demonstrated a clear mental image of what they wanted to see and hear in student performances, and each used modeling, comparison, and questioning techniques to develop awareness skills in their students. The findings have implications in teacher education and teacher development in music. (Contains 1 table, 1 figure, and 1 note.)