Fannie Mae and Freddie Mac are government-sponsored enterprises (GSEs) that play a crucial role in the U.S. housing finance system by providing liquidity, stability, and affordability to the mortgage market. They buy mortgages from lenders, package them into mortgage-backed securities, and sell these securities to investors, which helps to ensure that banks have enough capital to issue new loans. Their operations became particularly significant during the Great Recession as they were placed under conservatorship due to severe financial distress.