Fannie Mae is an indispensable part of American real estate industry. It operates in the secondary mortgage market in the United States, ensuring that mortgage banks and other lending institutions have enough funds to lend to buyers at low interest rates. Although Fannie Mae does not provide loans directly to homebuyers, it supports mortgage funds by purchasing mortgages from various lending institutions, which provide loans directly to homebuyers. Lending institutions that do business with Fannie Mae are an indispensable part of the primary mortgage market. Primary market lenders include mortgage companies, deposit and loan institutions, commercial banks, credit cooperatives and national and local housing credit institutions. These lenders sell mortgages in the secondary market. Secondary market investors include Fannie Mae, various pension funds, insurance companies, securities dealers and other financial institutions. Fannie Mae's task is to provide borrowers with a stable flow of mortgage loans. Fannie Mae provides the following three services to the market through three main business departments: mortgage portfolio, single-person family guarantee, residential and community development: Fannie Mae also provides financing support for lending institutions to develop apartment buildings and other rental houses, especially affordable housing.