Fannie Mae (also known as Federal National Mortgage Association) is a company that specializes in mortgage financing. It operates in residential mortgage markets and the global securities market. The company has two business segments: Single-Family and Multifamily. The Single-Family business operates in the secondary mortgage market relating to single-family mortgage loans, which are secured by properties containing four or fewer residential dwelling units. The Multifamily business operates in the secondary mortgage market relating primarily to multifamily mortgage loans, which are secured by properties containing five or more residential units.