Research has found that high-quality preparation and professional development improve principals’ effectiveness and are associated with increased teacher retention and student achievement in the schools those principals serve. However, not all principals have sufficient access to high-quality learning, and differences across states reflect varied state policies. This brief examines how state and district policies influence principals’ access to high-quality learning opportunities during preparation and throughout their careers. It identifies a set of policy levers that states and districts can adopt to promote principal effectiveness. These include standards for leadership practices, preparation programs, and licensure and investments in induction programs, leadership pipeline programs, and professional development.