This research report series from The Wallace Foundation demonstrates how school districts have planned and developed principal pipelines that last. The first report discusses the approaches, opportunities, and challenges encountered by 84 school districts in designing and implementing systematic principal pipelines. By analyzing the seven key domains of the pipelines—including leader standards, high-quality preparation, selective hiring, on-the-job support, supervisors, leadership tracking systems, and sustainability—the authors are able to pinpoint the status of these pipelines and how they helped build equity. The second report focuses on four pillars that districts can work within to create long-lasting pipelines, finding that strong leadership, clear communication, and institutional support were common components across all successful programs, operating under a framework of long-term sustainability.