Information technology can increase energy efficiency by improving the control ofenergy-using devices and systems. Awareness of this potential is not new—ideas for applications of information technology for energy efficiency have been promoted for more than 20 years. Butmuch of the potential gain from the application of information technology has not yet been realized. In an earlier paper one of the authors discussed some reasons for the slow exploitation of information technology’s potential to increase energy efficiency. The earlier paper also suggested that a combination of new requirements for the operation of the electricity system andthe development of new technology could cause a rapid increase in the pace of adoption. In this paper we describe an application of these ideas to the operation of a commercial building. First, we review basic concepts with emphasis on an open software-architecture. Then we describe thecomponents of this open software-architecture and its ability, for example, to nimbly add sensors and add control algorithms within a proprietary Building Automation System (BAS). Finally, wedescribe results from this application to Sutardja Dai Hall at the University of California Berkeley. Results include demonstration of reduced peak demand by 20 -30% and continuous energy savings of 20%.