Mortgage Finance Industry
Mortgage lending is a major category of the business of finance in the United States of America. Mortgages are commercial paper and can be conveyed and assigned freely to other holders. In the U.S., the Federal Housing Administration administers the programs colloquially known as "Ginnie Mae", Fannie Mae and "Freddie Mac" (also known as the GSEs or government sponsored entities) to foster mortgage lending and thus to encourage home ownership and construction.
These programs work by buying a large number of mortgages from banks and issuing (at a slightly lower interest rate) "mortgage-backed bonds" to investors. This allows the banks to quickly relend the money to other borrowers (including in the form of mortgages) and thereby to create more mortgages than the banks could with the amount they have on deposit. This in turn allows the public to use these mortgages to purchase homes, something the government wishes to encourage. The investors, meanwhile, gain low-risk income at a higher interest rate (essentially the mortgage rate, minus the cuts of the bank and GSE) than they could gain from most other bonds.