The Centers for Medicare & Medicaid Services (CMS) is the largest US payer of fee-for-service health care claims. However, health care providers have had, at best, limited access to Medicare fee-for-service data because CMS has not made the information broadly accessible. Access to Medicare fee-for-service data could help increase efficiency in health care delivery, reduce costs, and improve the quality of care. Recent remedies have taken shape as part of implementing the Affordable Care Act (ACA), but have yet to bear much fruit.