The reauthorization of the U.S. Elementary and Secondary Education Act, referred to as the Every Student Succeeds Act (ESSA), emphasizes evidence-based initiatives while providing new flexibilities to states and districts with regard to the use of federal funds, including funds to promote effective school leadership. This report describes the opportunities for supporting school leadership under ESSA, discusses the standards of evidence under ESSA, and synthesizes the research base with respect to those standards. The information can guide federal, state, and district education policymakers on the use of research-based school-leadership interventions; help them identify examples of improvement activities that should be allowable under ESSA; and support the rollout of such interventions. A second volume will further summarize the evidence and provide tools to help policymakers and practitioners make decisions about school-leadership-improvement activities under ESSA. This report includes notes and a bibliography.