Recently, there has been growing attention on the importance of the staff involvement component of a comprehensive school physical activity program (CSPAP). In particular, classroom teachers (CTs) are increasingly being called upon to promote physical activity (PA) in their classrooms as part of the PA during school component of a CSPAP. Consistent with this view, a burgeoning research base highlights several theoretical perspectives that provide insight into key factors associated with CTs' classroom-based PA promotion. The purpose of this article is to provide an up-to-date, comprehensive review of the theoretically framed research on CTs' classroom-based PA promotion and consider the implications of this research for the design of in-service professional development trainings that can be used to maximize staff involvement in CSPAPs.