Cities across America are making ambitious commitments to achieving 100% clean energy, decarbonization, and steep reductions in greenhouse gas emissions. The challenge now is to fulfill these commitments in a technically sound, cost-effective, and equitable way. For those tasked with taking action on these goals, such as city climate and sustainability officers, this two-page document from IMT explains how reducing energy use in buildings is a vital and necessary part of meeting this challenge. In addition to providing top takeaways, it includes specific recommended city actions on energy efficiency.