Moody's Investors Service, often referred to as Moody's, is the bond credit rating business of Moody's Corporation, representing the company's traditional line of business and its historical name. Moody's Investors Service provides international financial research on bonds issued by commercial and government entities.

The company ranks the creditworthiness of borrowers using a standardized ratings scale which measures expected investor loss in the event of default. Moody's Investors Service rates debt securities in several bond market segments. These include government, municipal and corporate bonds; managed investments such as money market funds and fixed-income funds; financial institutions including banks and non-bank finance companies; and asset classes in structured finance. In Moody's Investors Service's ratings system, securities are assigned a rating from Aaa to C, with Aaa being the highest quality and C the lowest quality.