Centers for Medicare & Medicaid Services (CMS)
The Centers for Medicare & Medicaid Services (CMS) is the US federal agency, part of HHS, that runs Medicare and oversees Medicaid, CHIP and the federal health insurance marketplace. It sets many of the rules health plans follow for provider directories and networks.
What does CMS do that affects provider data?
CMS sets network adequacy standards for Medicare Advantage, reviews plan directories, requires many payers to publish directory data through APIs, runs the NPI system (NPPES), and from 2026 shows Medicare Advantage directories in Medicare Plan Finder.
Has CMS checked directory accuracy?
Yes. Its Online Provider Directory Reviews of Medicare Advantage plans, published between 2017 and 2018, found widespread errors. In the third round, 48.74% of provider locations had at least one inaccuracy.
Where do CMS rules live?
In the Code of Federal Regulations, Title 42, and in rules published in the Federal Register, such as the contract year 2026 rule that brought directory data into Medicare Plan Finder.