Vacant and unattended residential properties can attract crime, cause blight, and pose a threat to public safety. While homeowners or mortgage owners--including the mortgage servicers that administer loans on behalf of loan owners--are responsible for maintaining vacant properties with mortgages undergoing foreclosure, the costs local governments incur to mitigate any unsafe conditions can be significant. GAO was asked to examine (1) trends in the number of vacant properties and how they relate to the recent increase in foreclosures, (2) the types of costs that vacant properties create and who bears the responsibility for these properties and their costs, and (3) state and local government strategies to address vacant properties and the federal role in assisting these efforts. GAO analyzed Census Bureau vacancy data and data on property maintenance costs from the Federal Housing Administration (FHA) and two housing-related government-sponsored enterprises (GSE). GAO conducted case studies in nine cities selected to provide a range of local economic and housing conditions, rates of foreclosure, and geographic locations. GAO also interviewed local officials, representatives of community development organizations, federal agencies, and mortgage servicers, among others. The Federal Reserve, Census, Office of Comptroller of the Currency, FHA, Federal Housing Finance Agency, and GSEs provided technical comments, which GAO incorporated as appropriate. Treasury commented that the report was informative and noted the need for all stakeholders to analyze policy responses to this issue.