Fannie Mae and Freddie Mac are the two largest companies that purchase mortgages from other lenders in the United States. Many lenders will underwrite their files according to their guidelines, but to ensure the eligibility to be purchased by Fannie Mae and Freddie Mac, underwriters will utilize what is called automated underwriting. This is a tool available to lenders to provide recommendations on the risk of a loan and borrower and it provides the amount of documentation needed to verify the risk.