The Federal National Mortgage Association (FNMA), commonly known as Fannie Mae, is a United States government-sponsored enterprise (GSE) and, since 1968, a publicly traded company. Founded in 1938 during the Great Depression as part of the New Deal, the corporation's purpose is to expand the secondary mortgage market by securitizing mortgage loans in the form of mortgage-backed securities (MBS), allowing lenders to reinvest their assets into more lending and in effect increasing the number of lenders in the mortgage market by reducing the reliance on locally based savings and loan associations. Its brother organization is the Federal Home Loan Mortgage Corporation (FHLMC), better known as Freddie Mac.

A mortgage-backed security (MBS) is a type of asset-backed security which is secured by a mortgage or collection of mortgages. The mortgages are aggregated and sold to a group of individuals that securitizes, or packages, the loans together into a security that investors can buy. Bonds securitizing mortgages are usually treated as a separate class, termed residential; another class is commercial, depending on whether the underlying asset is mortgages owned by borrowers or assets for commercial purposes ranging from office space to multi-dwelling buildings.