A brief history of the Common Information Model (CIM) is discussed. The first such group to take up the effort was the Energy Management System (EMS) Architecture Task Force. The EMS Architecture Task Force met at PES meetings roughly from 1982 to 1989. A final report was written, and the task force was disbanded. The next, much larger, effort was headed by the Electric Power Research Institute (EPRI ) project, the Control Center Applications Program Interface (CCAPI), which started in the early 1990s. To allow the 'plug and play' capabilities sought by both the EMS Architecture Task Force and the CCAPI project, the EPRI teams began to design an application program interface (API). Instead of concentrating on the API details that have to do with a vendor?s computers, operating system, etc., the team began the effort to develop the framework for the meaning and structure of the information exchanged between the EMS database and various applications. A parallel effort that also contributed to the CIM development was the EPRI Operator Training Simulator (OTS) project, which had the goal of developing a training simulator that could be used by any EPRI member. The Unified Modeling Language (UML) was chosen as the language to represent the CIM semantics. In 2006, EPRI initiated the CIM for planning models with the objective of developing a common power system network model that both operations and planning groups can use as a basis for information exchange.