The Federal Housing Finance Agency (FHFA or Agency) is issuing a final rule to improve the liquidity of the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corporation (Freddie Mac) (collectively, the Enterprises) To-Be-Announced (TBA) eligible mortgage-backed securities (MBS) by requiring the Enterprises to maintain policies that promote aligned investor cash flows for both current TBA-eligible MBS, and, upon its implementation, for the Uniform Mortgage-Backed Security (UMBS)--a common, fungible MBS that will be eligible for trading in the TBA market for fixed-rate mortgage loans backed by one-to-four unit (single-family) properties. The final rule codifies alignment requirements that FHFA implemented under the Fannie Mae and Freddie Mac conservatorships. The rule is integral to the successful transition to and ongoing fungibility of the UMBS. FHFA has announced that the Enterprises will begin issuing UMBS in place of their current TBA-eligible securities on June 3, 2019.