American Capital Agency Corp. operates as a real estate investment trust (REIT) in the United States. The Company's income comes primarily from its investments in agency mortgage-backed securities (agency MBS). The Company's investments consist of residential mortgage pass-through securities and collateralized mortgage obligations (CMOs) guaranteed by a government-sponsored enterprise, such as the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corporation (Freddie Mac), or by a United States Government agency, such as the Government National Mortgage Association (Ginnie Mae). It also invests in agency debenture securities issued by Freddie Mac, Fannie Mae or the Federal Home Loan Bank and in other agency securities. The Company is externally managed by American Capital AGNC Management, LLC, an affiliate of American Capital, Ltd.