Mortgage bonds issued by American mortgage agencies Freddie Mac and Fannie Mae. These two institutions combine the mortgage loans guaranteed by the Federal Housing Commission or other financial institutions according to the term and interest rate, issue mortgage bonds as collateral or guarantee, sell them in the financial market, and then use the income funds to provide housing loans to more people. At the same time, it also provides guarantees for the types of mortgage securities issued by financial institutions that provide housing loans. The important products issued are mortgage-backed securities or mortgage transfer.