The purpose of this study was to examine interactions among in-service music teachers in a graduate music teacher education programme using Wenger, McDermott, and Snyder's [2002. "Cultivating Communities of Practice: A Guide to Managing Knowledge." Boston, MA: Harvard Business School Press] Communities of Practice (CoPs) framework. The results revealed that a music teacher interaction in a graduate music education programme evolved into CoPs. The domain, teachers' shared understanding of their practice, indicated that music teachers wanted to become better educators of their subjects. Music teachers in an INSTEP (Intensive Summer Teacher Education Program) understood that class materials would be helpful for their teaching and students, so they actively participated in interaction among classmates and shared their own knowledge and teaching experiences, which was defined as the practice. Also, through the cohort structure and group projects, music teachers continuously interacted with other colleagues, and this regular interaction in INSTEP classes, defined as the community, enabled a deeper level of community sense, also referred to as CoPs.