Bond insurance

This is a service whereby issuers of a bond can pay a premium to a third party, who will provide interest and capital repayments as specified in the bond in the event of the failure of the issuer to do so. The effect of this is to raise the rating of the bond to the rating of the insurer; accordingly, a bond insurer's credit rating must be almost perfect.
The premium requested for insurance on a bond is a measure of the perceived risk of failure of the issuer.
Government bonds are almost never insured; municipal bond insurance was introduced in the US in 1971, and by 2002 over 40% of municipal bonds were insured, often by a procedure involving payment of a single premium at the purchase of the bond.