Reducing errors in diagnosis is the next big challenge for patient safety. Diagnostic safety improvement efforts should become a priority for health care organizations, payers, and accrediting bodies; however, external incentives, policies, and practical guidance to develop these efforts are largely absent. In this Perspective, the authors highlight ways in which health care organizations can pursue learning and exploration of diagnostic excellence (LEDE). Building on current evidence and their recent experiences in developing such a learning organization at Geisinger, the authors propose a 5-point action plan and corresponding policy levers to support development of LEDE organizations. These recommendations, which are applicable to many health care organizations, include (1) implementing a virtual hub to coordinate organizational activities for improving diagnosis, such as identifying risks and prioritizing interventions that cross intra-institutional silos while promoting a culture of learning and safety; (2) participating in novel scientific initiatives to generate and translate evidence, given the rapidly evolving "basic science" of diagnostic excellence; (3) avoiding the "tyranny of metrics" by focusing on measurement for improvement rather than using measures to reward or punish; (4) engaging clinicians in activities for improving diagnosis and framing missed opportunities positively as learning opportunities rather than negatively as errors; and (5) developing an accountable culture of engaging and learning from patients, who are often underexplored sources of information. The authors also outline specific policy actions to support organizations in implementing these recommendations. They suggest this action plan can stimulate scientific, practice, and policy progress needed for achieving diagnostic excellence and reducing preventable patient harm.