This report presents the results of a state-by-state analysis of the potential energy and cost savings from improving compliance with building energy codes to 100 percent from current levels. The report also examines 45 statewide compliance evaluation studies, providing a summary of evaluation methods and key findings. Evidence in most states indicates that staggering rates of non-compliance, as high as 100 percent in some jurisdictions, have eroded the gains from energy code development and adoption. The projected national savings from bringing just a year’s worth of new residential and commercial construction in the U.S. up to full compliance is 2.8-8.5 quadrillion Btu annually, or $63-$189 million in annual energy cost savings. This equates to lifetime savings of up to $37.1 billion. The magnitude of the energy code-compliance problem presents a significant opportunity for policymakers and energy efficiency program administrators to save homeowners and businesses billions of dollars in energy costs simply by improving enforcement of existing building energy codes