Issued by corporations, junk bonds are of less than investment-grade ratings (i.e., below a Baa rating by Moody's or BBB by Standard & Poor's). Because the credit risk in owning them is greater than higher-quality bonds, their yields are often higher. These bonds came into prominence as a financing mechanism for the mergers and acquisitions that have taken place. The money that a company gets from selling junk bonds is normally used to retire the debt incurred in an acquisition.