The benefits of energy efficiency are apparent—it saves the environment—but as it turns out, it saves us money too. A new report from the International Energy Agency says investments in energy efficiency could return upwards of $18 trillion—which is just about equal to the combined total of all of North America’s economies. The research showed that for every dollar invested in energy efficiency there is a possible return of up to 2.5 times that amount in terms of productivity gains. A key aspect of the report was a shift in defining energy efficiency from energy not used, to a “first fuel” definition where all the environmental and social impacts of energy efficiency are taken into account.