This study is structured around two objectives: surveying the 180 years’ evolution of the US mortgage intermediation system (MIS); and, extracting the lessons to be learned by emerging mortgage markets. To that end, I first discuss three pillars of a well-functioning MIS as a conceptual underpinning – intermediation efficiency, affordability enhancement, and risk management. The historical survey proceeds based on four reasonably distinct time periods. The US Mortgage Intermediation System (henceforth, the USMIS) is one of the largest and most complicated financial systems in the world. It manages an extensive portfolio of $8.8 trillion mortgage debt outstanding (MDO) as of the end of third quarter of 2005, which amounts to nearly 70% of nominal GDP during the period; is highly efficient with the competitive primary market for loan production and servicing and with the liquid secondary market for funding; and, offers consumers with various affordable loan products such as high LTV loans for wealth-constrained households, subprime mortgages for those with impaired credit records, and reverse annuity loans for house-rich cash-poor senior citizens. In recent years, the system also served as a stabilizer to the macro economy, as evidenced by several studies. That is, aided by the strong home price appreciation and the low mortgage interest rates since the late 1990s, the USMIS enabled a large number of households to liquidity their home equities for consumer spending and for capital investment (Case, Quigley, and Shiller (2001) and Leung and Zeng (2005)) The net mortgage equity extraction – the total amount of newly-originated loans minus the total repaid loans – also jumped to $800 billion in 2004, about 170% increase from $300 billion in 2000.