A substantial and growing body of research suggests that strong school leadership is critical for shaping productive learning environments, supporting high-quality teachers and teaching, and influencing student outcomes. But what characteristics contribute to high-quality principal preparation programs and learning experiences? And to what extent do principals have opportunities to participate in these experiences? This report reviews the research literature (2000-2017) to understand the elements of high-quality programs and learning experiences that have been associated with positive outcomes, including principals' sense of preparedness, efficacy, and reported practices, staff perceptions of school climate, teacher retention, and student achievement. It also examines the extent to which principals have opportunities to participate in learning experiences with those elements and the policies that drive both the development of high-quality programs and access to them. Through this review, key findings, research implications, and policy implications related to principal preparation and training emerge. [For the technical supplement, see ED620193.]