The U.S. Postal Service (Postal Service) recently installed Energy Information Systems (EIS) at 30 facilities in California. These systems integrate electric utility meter data acquisition hardware, software, and communication systems to collect, archive, analyze, and display whole-facility energy consumption data. At some point in the future, these systems could also be integrated with sub-meters that measure the electricity consumption of key end-use equipment. The purpose of this guidebook is to help Postal Service facility managers interpret and act upon energy data available from their EIS, translating the abundance of information these systems provide into knowledge that can be used to reduce energy use and costs. The guidebook first describes basic EIS capabilities and explains the data and reports that Postal Service EIS provide. It outlines a set of strategies for utilizing this information to improve operations and maintenance of building energy use equipment and for facilitating demand response. Finally, the guidebook offers suggestions on creating a routine for tracking and analyzing energy data and integrating this information into regular energy management activities.