This comprehensive policy brief emphasizes the importance of addressing diagnostic errors through health policy change. The report explores the role of missed and delayed diagnosis in malpractice claims and preventable harm to patients. The authors note the lack of attention to diagnosis in the seminal To Err is Human report. They outline several strategies to detect and characterize diagnostic errors, including patient and provider surveys, case review, voluntary reporting, claims review, audits, and trigger tools in electronic medical records. To enhance timely and accurate diagnoses, the report advocates for increasing research funding, greater government oversight, instituting formal diagnostic feedback mechanisms, and payment and medical education reform.