This product of the Regional Energy Efficiency Organizations (REEOs) was developed to help inform national stakeholders about the strategies that have been used to achieve deep energy savings in the multifamily housing sector through energy efficiency upgrades. These strategies could be used as a model in areas across the country where utility program administrators and policymakers seek to achieve deep energy savings in the multifamily building stock for the purposes of reducing energy costs, creating comfortable and healthy homes, meeting regulatory requirements, or reducing the environmental impacts of energy consumption. This report includes a national multifamily market characterization, barriers and opportunities for program and policy efforts, and eight exemplary case studies from across the country. This report was made possible by the generous support of the John D. and Catherine T. MacArthur Foundation.