This report, the first international assessment of this type, investigates the life-cycle environmental and natural resource implications of large-scale deployment of energy efficiency technologies. The report examines more than 30 demand-side energy efficiency technologies across different technological clusters, including lighting, buildings, information and communication technology, efficient metals processing, high-efficiency co-generation, and transportation. In addition, the combined effects of low-carbon energy supply and deployment of efficient demand-side technologies under the 2 degree and 6 degree Celsius scenarios are assessed. Research confirms that demand-side technologies reduce greenhouse gas emissions as well as many other environmental impacts. However, the magnitude of those improvements varies widely among technologies and regions. In some cases, demand-side technologies may increase resource consumption and even greenhouse gas emissions. Therefore, it is crucial to understand where, when, and with which technology investment should be placed to maximize benefits.