Teacher professional development (PD) is often extended as a driver of good teaching and effective schools. In recent years, teacher PD has increasingly focused on developing teacher social capital by placing teachers within professional communities to collectively solve instructional problems. Using Bourdieu's and Coleman's conceptions of social capital as a theoretical and practical lens, this article explores how a social capital frame could generate more effective PD policy in music education. Areas examined also include the specific ways in which social capital becomes a lever for teacher growth and school improvement and the social dimensions of music teacher PD. The article concludes with principles of social capital-advancing PD policy, examples of principle-aligned PD policies, implications for research and advocacy, and an accounting of challenges and opportunities for the future. The author argues that centralizing social capital development as an aim of PD represents a new frontier in music teacher learning.