The $13.6 billion appropriation of stimulus funds under the American Recovery and Reinvestment Act of 2009 (ARRA) included approximately $3 billion for the modernization and renovation of the nation’s public housing stock. In addition, the U.S. Department of Housing and Urban Development (HUD) disbursed $600 million through competitive grants supporting energy efficiency or green building in public housing, and $250 million to establish the Green Retrofit Program (GRP) that provided loans and grants to privately owned assisted multifamily housing. This study estimates the energy and water savings achieved by the program grantees as a result of the ARRA-funded retrofit investments. The report describes the preliminary energy savings model, data used to validate the model, and an energy savings tool that was developed to help HUD predict the value earned from future retrofit investments. The report further makes recommendations for future green investment programs and evaluations. The evidence suggests that HUD’s ARRA-supported green investments were able to achieve substantial energy and water savings, significant environmental improvements, and extensive revitalization of the nation’s public and assisted housing stock.