Overseen by the US Securities and Exchange Commission.

http://www.sec.gov/answers/nrsro.htm

A Nationally Recognized Statistical Rating Organization (NRSRO) is a credit rating agency (CRA) that issues credit ratings that the US Securities and Exchange Commission (SEC) permits other financial firms to use for certain regulatory purposes.

Under the Credit Rating Agency Reform Act, an NRSRO may be registered with respect to up to five classes of credit ratings: (1) financial institutions, brokers, or dealers; (2) insurance companies; (3) corporate issuers; (4) issuers of asset-backed securities; and (5) issuers of government securities, municipal securities, or securities issued by a foreign government.

List of NRSROs SEC Spotlight on NRSROs

Entities that rate US institutional debt that are registered with the Securities and Exchange Commission.

http://en.wikipedia.org/wiki/Nationally_recognized_statistical_rating_organization