In October 1997, Congress enacted the Multifamily Assisted Housing Reform and Affordability Act (MAHRA), commonly referred to as the "mark-to-market" legislation. The most significant housing legislation in a decade, MAHRA seeks to cut Section 8 subsidy costs on about 4,000 properties, bringing rents into line with local markets. MAHRA provides a broad framework for resetting rents and resizing mortgages and answers many fundamental policy questions. The U.S. Department of Housing and Urban Development's (HUD's) evolving program rules will determine how the mark-to-market legislation will actually work, who will participate, and what will happen to the properties and their residents. This article describes the legislation's origins, major features, and properties affected and reviews the key policy issues. To illustrate the dynamics, three distinct implementation options are presented as thought experiments. This article also explores potential roles for nonprofit entities and concludes by reviewing HUD's recently issued regulations.