At long last, scholars and policy makers have come to realize what most school administrators have known for years--that effective schools require both outstanding teachers and strong leaders. Although there is considerable research about the characteristics of effective school leaders and the strategies principals can use to help manage increasingly diverse roles, comparatively little is known about how to design programs that can develop and sustain effective leadership practices. In an effort to increase the knowledge about professional development programs, the Wallace Foundation recently commissioned a study of innovative principal professional development programs and the policy and funding mechanisms that support them. In fall 2003, a team of researchers from the Stanford School of Education was awarded a Wallace grant and proceeded to design and embark upon a nationwide study of both the pre- and in-service professional development of school principals. This article discusses the findings about the qualities and impact of strong programs from a study of professional development for principals.