School leaders are critical in the lives of students and to the development of their teachers. Unfortunately, in too many instances, principals are effective in spite of--rather than because of--district conditions. To truly improve student achievement for all students across the country, well-prepared principals need the tools, support, and culture that enable them to be the best. New Leaders and the Bush Institute's Alliance to Reform Educational Leadership (AREL) launched the Conditions for Effective Leadership Project and partnered with leading researchers and practitioners to generate a comprehensive and research-based framework outlining the conditions necessary for transformational school leaders to succeed. The project used a combination of literature review, empirical data collection, and expert convenings to build consensus and bundle the disparate ideas into a single framework that is accessible to school system leaders. This report describes that set of conditions that effective school systems have in place that enable principals to be successful. The conditions include four strands developed as follows: Strand 1: Alignment among goals, strategies, structures, and resources; Strand 2: Culture of collective responsibility, balanced autonomy, and continuous learning and improvement; Strand 3: Effective management and support for principals; and Strand 4: Systems and policies to effectively manage talent at the school-level. [See accompanying report: "Great Principals at Scale: Toolkit" at ED556350.]