Also known as monoline insurers. This is an insurance company that guarantees the timely repayment of bond interest and principal in exchange for insurance premiums. When a bond issuer defaults, the monoline is obligated to make all interest and principal payments when due (the underlying obligation is not, however, accelerated). These companies originally only guaranteed bonds issued by municipalities. However, their business expanded to include other financial products such as project bonds (bonds issued by a project company in a project finance transaction) and collateralized debt obligations (CDOs). As a result of the 2007 subprime mortgage crisis, the credit rating of many monolines was downgraded because of their exposure to mortgage-backed securities, undermining their ability to guarantee financial products. These insurance companies are called monolines because they underwrite only financial products. They do not provide insurance products such as life, property, or casualty insurance. A bond that is guaranteed by a monoline is known as a wrapped bond.