This chapter in The Handbook of Mortgage-Backed Securities explains

• causes and extent of growth in the non-agency RMBS market until 2007; 
• factors contributing to the crisis in the RMBS market that began in 2007; 
• the key events of the financial crisis affecting mortgage-backed securities; 
•  the role of the government-sponsored enterprises (GSEs) in the mortgage origination and MBS markets, particularly during and just after the financial crisis; 
• federal government policies and programs to support the US mortgage finance system during and after the crisis; and
• how the mortgage finance system has changed as a result of the crisis.