The growth of the secondary market has thus given mortgage lenders greater access to the capital markets, lowered transaction costs, and spread risk more broadly, thereby increasing the supply of mortgage credit to all types of households
The recent sharp increases in subprime mortgage loan delinquencies and in the number of homes entering foreclosure raise important economic, social, and regulatory issues. Today I will address a series of questions related to these developments. Why have delinquencies and initiations of foreclosure proceedings risen so sharply? How have subprime mortgage markets adjusted? How have Federal Reserve and other policymakers responded, and what additional actions might be considered? How might the problems in the market for subprime mortgages affect housing markets and the economy more broadly?
The Development of the Subprime Mortgage MarketLet me begin with some background. Subprime mortgages are loans made to borrowers who are perceived to have high credit risk, often because they lack a strong credit history or have other characteristics that are associated with high probabilities of default. Having emerged more than two decades ago, subprime mortgage lending began to expand in earnest in the mid-1990s, the expansion spurred in large part by innovations that reduced the costs for lenders of assessing and pricing risks. In particular, technological advances facilitated credit scoring by making it easier for lenders to collect and disseminate information on the creditworthiness of prospective borrowers. In addition, lenders developed new techniques for using this information to determine underwriting standards, set interest rates, and manage their risks.
The ongoing growth and development of the secondary mortgage market has reinforced the effect of these innovations. Whereas once most lenders held mortgages on their books until the loans were repaid, regulatory changes and other developments have permitted lenders to more easily sell mortgages to financial intermediaries, who in turn pool mortgages and sell the cash flows as structured securities. These securities typically offer various risk profiles and durations to meet the investment strategies of a wide range of investors.
These factors laid the groundwork for an expansion of higher-risk mortgage lending over the past fifteen years or so. Growth in the market has not proceeded at a uniform pace, but on net it has been dramatic. About 7-1/2 million first-lien subprime mortgages are now outstanding, accounting for about 14 percent of all first-lien mortgages. 1 So-called near-prime loans–loans to borrowers who typically have higher credit scores than subprime borrowers but whose applications may have other higher-risk aspects–account for an additional 8 to 10 percent of mortgages. 2
For borrowers, the consequences of defaulting can be severe–possibly including foreclosure, the loss of accumulated home equity, and reduced access to credit
The expansion of subprime mortgage lending has made homeownership possible for households that in the past might not have qualified for a mortgage and has thereby contributed to the rise in the homeownership rate since the mid-1990s. In 2006, 69 percent of households owned their homes; in 1995, 65 percent did. The increase in homeownership has been broadly based, but minority households and households in lower-income census tracts have recorded some of the largest gains in percentage terms. Not only the new homeowners but also their communities have benefited from these trends. Studies point to various ways in which homeownership helps strengthen neighborhoods. For example, homeowners are more likely than renters to maintain their properties and to participate in civic organizations. Homeownership has also helped many families build wealth, and accumulated home equity may serve as a financial reserve that can be tapped as needed at a lower cost than most other forms of credit.
Broader access to mortgage credit is not without its downside, however. Not surprisingly, in light of their 
weaker credit histories and financial conditions, subprime borrowers face higher costs of borrowing than prime borrowers do and are more likely to default than prime borrowers are. Their neighbors may suffer as well, as geographically concentrated foreclosures tend to reduce property values in the surrounding area.