Most bonds are allocated a credit rating to indicate to an investor the likelihood of a subsequent default...
Most bonds are allocated a credit rating to indicate to an investor the likelihood of a subsequent default. The three firms, or 'agencies' that specialise in awarding these ratings, Standard and Poors, Moody's and Fitch do so by looking at a number of factors that could increase or decrease this risk including the credit quality of the issuer, their ability to cover interest payments from profits and any security- usually in the form of assets such as property- on offer. The ratings then vary from AAA 'triple A' for safe, low risk bonds, typically issued by high quality institutions like the UK government and blue-chip companies, down to D for those which have failed to make a coupon payment on time and are therefore in default. Many fund managers are obliged by the regulator to hold 'investment grade' bonds meaning those with a credit rating of BBB and above.
See Tim Bennett's video tutorial: Do we need ratings agencies?