States and districts are embarking on efforts to improve school leadership as a lever to promote school improvement. Such efforts have a solid base of research attesting to their effectiveness, and some view them as particularly cost-effective because principals "can be powerful multipliers of effective teaching and leadership practices in schools." Although the logic of this perspective is sound, in truth, very little is known about the resources required to improve school leadership. This report fills an important gap in the literature on school leadership by presenting an approach for understanding the resources and expenditures associated with efforts to prepare, hire, evaluate, develop, and support school leaders and by presenting estimates of those resources and expenditures. All districts that employ more than a few school leaders devote at least some resources to these activities and might find some value to our approach. RAND Corporation analysts applied an approach to develop estimates of the resources required to put in place and operate "principal pipelines"--pipelines for preparing, hiring, supporting, and managing school leaders--based on data they collected from six urban districts that participated in The Wallace Foundation's Principal Pipeline Initiative. Technical details on data collection and analysis are qppended. [For the related report from The Wallace Foundation, see ED574748.]