The U.S. Agency market consists of issuers that are not direct obligations of the U.S. Treasury, but do involve government sponsorship or guarantees. Many of the agencies are referred to as Government-Sponsored Entities (GSEs); which is slightly misleading as there are numerous types of agencies, with varying degrees of government support. Below is a list of the five largest agency issuers and a general guideline to their degree of government sponsorship:

	Agency	Full faith and credit	Authority to borrow funds
	Federal National Mortgage Association (FNMA)	NO	YES
	Federal Home Loan Mortgage Corporation (FHLMC)	NO	YES
	Federal Home Loan Bank (FHLB)	NO	YES
	Government National Mortgage Association (GNMA)	YES	NO
	Student Loan Marketing Association (SLMA)	NO	YES

GNMA is the only one of the major agencies listed above that is directly guaranteed by the U.S. government, while the others have the ability to borrow from the government if needed. The two dominating issuers of bonds are the Federal National Mortgage Association (FNMA, a.k.a. Fannie Mae), and the Federal Home Loan Mortgage Corporation (FHLMC, a.k.a. Freddie Mac). Both agencies were established with the purpose of purchasing individual mortgage loans from mortgage lending institutions throughout the country to reduce the amount of loans in the mortgage lender's portfolio. The result is an increased availability of mortgage credit and lower overall mortgage rates. The Government National Mortgage Association (GNMA) has a similar mandate; however, their portfolio is composed of mortgages insured by the Federal Housing Administration (FHA), or guaranteed by the Veterans or Farmers Home Administration. All three agencies also participate in the packaged sale of mortgages from their portfolios in the form of mortgage-backed securities.