A mortgage-backed security (MBS) is an asset-backed security or debt obligation that represents a claim on the cash flows from mortgage loans, most commonly on residential property.
First, mortgage loans are purchased from banks, mortgage companies, and other originators. Then, these loans are assembled into pools. This is done by government agencies, government-sponsored enterprises (GSE), and private entities.
Mortgage-backed securities represent claims on the principal and payments on the loans in the pool, through a process known as Securitization. These securities are usually sold as bonds, but financial innovation has created a variety of securities that derive their ultimate value from mortgage pools.
Most MBSs are issued by the Government National Mortgage Association (Ginnie Mae), a U.S. government agency, or the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corporation (Freddie Mac), U.S. government-sponsored enterprises.
Ginnie Mae, backed by the full faith and credit of the U.S. government, guarantees that investors receive timely payments. Fannie Mae and Freddie Mac also provide certain guarantees and, while not backed by the full faith and credit of the U.S. government, have special authority to borrow from the U.S. Treasury. Some private institutions, such as brokerage firms, banks, and homebuilders, also securitize mortgages, known as "private-label" mortgage securities.
Residential mortgages in the United States have the option to pay more than the required monthly payment (curtailment) or to pay off the loan in its entirety (prepayment). Because curtailment and prepayment affect the remaining loan principal, the monthly cash flow of an MBS is not known in advance, and therefore presents an additional risk to MBS investors.
Commercial mortgage-backed securities (CMBS) are secured by commercial and multifamily properties (such as apartment buildings, retail or office properties, hotels, schools, industrial properties and other commercial sites). The properties of these loans vary, with longer-term loans (5 years or longer) often being at fixed interest rates and having restrictions on prepayment, while shorter-term loans (1–3 years) are usually at variable rates and freely pre-payable.
- State Street Sells $11 Billion in Mortgage Securities Bloomberg, December 9, 2010