In this brief, the authors assess the move by Fannie Mae and Freddie Mac to a single security, called the Uniform Mortgage-Backed Security (UMBS). After discussing the purpose of the single security, the authors review its success to date, the challenges that remain, and a recent proposal by the Federal Housing Finance Agency (FHFA) to address those challenges. The authors also offer thoughts on how the FHFA might use a more market-oriented approach to address the challenges more effectively.