Often principals in urban school districts report to a central office staff person whose primary function is to supervise principals. Over the past decade, the principal supervisor role has shifted away from administrative oversight toward developing principals’ instructional leadership capacity. As principals are increasingly responsible for driving improvement in their schools, the demands of supervising principals similarly have changed. This chapter examines the ways in which principal supervisors developed and supported principals’ instructional leadership analyzing over 200 interviews collected in 6 urban school districts that participated in the Principal Supervisor Initiative. These districts shifted principal supervision from a traditional administrative oversight model to one focused on principal development and support. The chapter describes the activities, practices, and routines that grounded the work of principals and their supervisors, and demonstrates the importance of supervisors’ own learning to develop the skills necessary to carry out the new role and build consistency of practice.