The period following the 2001 recession through 2006 is rightly called a housing boom. House prices and net borrowing by households surged in the early part of the decade, easily outpacing growth in household income. But, with the onset of the financial crisis and the failure of many mortgage market participants, access to mortgage finance declined dramatically. This Economic Letter summarizes some of the key ways that the mortgage market evolved during the boom years and during the ensuing housing market bust. It focuses on changes in the way loans were made and funded and how loan characteristics themselves changed.