An energy management system (energy management system - EMS) is a computer-aided system of tools used by utility operators (typically electric power, gas or water companies) to monitor, control and optimize the performance of the generation and/or transmission of the service. They can be used in systems of various scales, managing microgrids or microgrids.[1][2]​.

As a computer technology it has great overlap with SCADA systems, which is why they are also known together as SCADA/EMS or EMS/SCADA. In this sense, the EMS terminology excludes monitoring and control functions, but more specifically refers to the set of energy generation and transportation planning activities. EMS manufacturers also typically supply a corresponding dispatcher training simulator (DTS). This related technology makes use of SCADA and EMS components as a training tool for dispatch center operators.

Commercial energy management systems are also typically used by individual commercial entities to monitor, measure, and control the electrical loads of their buildings. Energy management systems can be used to centrally control devices such as HVAC units and lighting systems in multiple locations, such as stores, supermarkets, and restaurants. Energy management systems can also provide metering, submetering and monitoring functions that allow facility and building managers to collect data and insights that enable them to make more informed decisions about energy activities at their sites.

Until the early 1990s, EMS system vendors typically used vendor-proprietary hardware and operating systems. At that time, EMS vendors such as Harris Controls (now GE), Hitachi, Cebyc), Control Data Corporation, Siemens, and Toshiba manufactured their own proprietary hardware. EMS providers that did not manufacture their own hardware often relied on products developed by third parties such as Digital Equipment, Gould Electronics, and MODCOMP). Digital Equipment's VAX 11/780 was a popular choice among some EMS providers. EMS systems are now based on a model-based approach. Traditional planning models and EMS models were always maintained independently and were rarely synchronized with each other. Using EMS software allows planners and operators to share a common model, reducing the mismatch between the two and cutting model maintenance in half. Having a common user interface also allows for an easier transition of information from planning to operations.