A credit rating agency (CRA) is a company that assigns credit ratings for issuers of certain types of debt obligations as well as the debt instruments themselves. In some cases, the servicers of the underlying debt are also given ratings. In most cases, the issuers of securities are companies, special purpose entities, state and local governments, non-profit organizations, or national governments issuing debt-like securities (i.e., bonds) that can be traded on a secondary market. A credit rating for an issuer takes into consideration the issuer's credit worthiness (i.e., its ability to pay back a loan), and affects the interest rate applied to the particular security being issued. (In contrast to CRAs, a company that issues credit scores for individual credit-worthiness is generally called a credit bureau or consumer credit reporting agency.)

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