In this article, we apply the concept of systemness to music and arts teacher professional development (PD), arguing that to address perennial issues of access and scale, PD policy should be understood as a systems issue. Using systems theory as a lens and the robust and integrated PD system in Singapore as an exemplar, we address the following questions: What policies might ensure all music and arts teachers are provided high-quality PD opportunities? How might PD efforts be coordinated for comprehensive changes in music and arts teachers, for students, and for the profession writ large? We close by setting forth systems-minded PD policy recommendations for nations whose PD structures fail to meet the needs of all music and arts teachers.