Mortgage-backed securities (MBS) are products that bundle mortgages together and are traded like securities for sale on the markets.

Typically investment banks build these products by bundling mortgages with different interest rates and risk premiums, with the hope of the investor gaining a higher yield than can be found from traditional risk-free products, like U.S. Treasuries.

Mortgage-backed securities got an infamous name during the 2008 financial crisis, as many of the packaged loans were subprime in nature. Many MBS products lost incredible value during the crisis, particularly following ruling FAS 157, which required banks to mark their value to market.