Although diagnostic error is a well-recognized source of preventable patient harm, measuring and mitigating diagnostic error remains challenging. This National Quality Forum report describes the development of a framework to assist with measuring diagnostic quality and safety. The framework outlines 3 domains and 11 subdomains for measuring diagnostic quality and safety as well as 62 prioritized measure concepts. High-priority areas for measure development include timeliness of diagnosis, timely follow-up of test results, communication and handoffs, patient-reported diagnostic errors, and patient experience related to diagnostic care. The committee also identified several cross-cutting themes and makes recommendations for researchers seeking to develop measures to improve diagnostic safety. A PSNet perspective discussed challenges and opportunities regarding diagnostic error.