Ratings systems are usually applied to nonfinancial corporations, as special approaches are employed for banks and other financial institutions. First of all, we describe the rating systems of the two main credit rating agencies, Standard & Poor's and Moody's. Almost all of the public issues of debt instruments in the United States and Canada are rated by these agencies. Their ratings of public issues are made available to the public, as are the periodic revisions of these ratings. Companies and instruments are classified into discrete rating categories that correspond to the estimated likelihood of the company failing to pay its obligations.