The availability of computers at moderate costs and the concern for reducing energy consumption have resulted in the application of computer-based controllers to more than just industrial process applications. These controllers, commonly called energy management systems (EMS), can be used to control virtually all non-process energy using pieces of equipment in buildings and industrial plants. This chapter analyses the various types of energy management systems which are available and illustrates some of the methods used to reduce energy consumption. By concentrating the control of many items of equipment at a single point, the EMS allows the building operator to tailor building operation to precisely satisfy occupant needs. EMS with demand limiting capabilities utilize either pulses from the utility meter or current transformers to predict the facility demand during any demand interval. The chapter also illustrates a typical demand chart before and after the actions of a demand limiter.