The surge in mortgage foreclosures that began in late 2006 and continues today was initially driven by deterioration in the performance of nonprime (subprime and Alt-A) loans. Nonprime mortgage originations increased dramatically from 2000 through 2006, rising from about 12 percent ($125 billion) of all mortgage originations to about 34 percent ($1 trillion). The nonprime market contracted sharply in mid-2007, partly in response to increasing defaults and foreclosures for these loans. This report (1) provides information on the performance of nonprime loans through December 31, 2009; (2) examines how loan and borrower characteristics and economic conditions influenced the likelihood of default (including foreclosure) of nonprime loans; and (3) describes the features and limitations of primary sources of data on nonprime loan performance and borrower characteristics, and discusses federal government efforts to improve the availability or use of such data. To do this work, GAO analyzed a proprietary database of securitized nonprime loans and Home Mortgage Disclosure Act data, and reviewed information on mortgage data sources maintained by private firms and the federal government.