The Wallace Foundation's Principal Supervisor Initiative (PSI) was a four-year effort to redefine principal supervision in six urban school districts. Launched in 2014, the PSI aimed to help these districts transform the principal supervisor position from a role that traditionally focused on managerial tasks to one dedicated to developing and supporting principals to be effective instructional leaders. The PSI encouraged these districts to revise the principal supervisors' job description to focus on instructional leadership, reduce principal supervisors' span of control (the number of principals they oversee), train supervisors and develop their capacity to support principals, create systems to identify and train new supervisors, and strengthen central office structures to support and sustain changes in the principal supervisor's role. This report presents findings from a 2018 survey of principal supervisors in 54 urban school districts, including the 6 PSI districts. The districts were all members of the Council of the Great City Schools, a coalition of the nation's largest urban public school systems. In total, 343 principal supervisors responded to the survey, including 50 in the 6 PSI districts (a 96 percent response rate) and 293 in the 48 other urban districts (a 64 percent response rate). This report compares principal supervision in the PSI districts with that in other urban districts. It compares: (1) the "structures" districts put in place to support the principal supervisor role (including principal supervisors' span of control and districts' approaches to selecting and training supervisors); and (2) principal supervisors' "professional practices." This comparison can provide greater context for the changes that the PSI districts made during the initiative, highlighting areas where the PSI districts' work aligned with broader national trends and areas where it surpassed or lagged these trends. It can also provide a roadmap for other districts seeking to strengthen the principal supervisor role to better support principals as instructional leaders, by highlighting aspects of principal supervision that districts and states may find easier to change and aspects that may require more deliberate action and focus.