Energy efficiency programs have historically underserved multifamily housing for low-income households, largely because of the barriers this market presents to program administrators. This report examines 32 programs that target affordable multifamily buildings, focusing on energy savings, spending, participation, and cost effectiveness. We also describe the details of program designs that have proved effective in overcoming the unique challenges of this market. Our research shows that cost-effective affordable multifamily programs are saving energy, reducing costs, mitigating energy burdens, and improving quality of life for low-income households.