The California Independent System Operator Corporation (CAISO) is in charge of managing the electricity flow along California's open-market wholesale power grid. The CAISO implemented a nodal LMP Electricity Market based on the full network model and upgraded its infrastructure with new state of the art technology in 2009. The implementation of the new market system utilized the Service Oriented Architecture (SOA) and enterprise service bus-based technology to integrate many of the CAISO systems to assure grid reliability and efficient and economic operation of the electricity market. The CAISO systems are acquired from different application vendors and this created an integration challenge. This paper summarizes how CAISO leverages IEC TC57 Common Information Model (CIM) for the network models and enterprise wide messaging in integrating different applications from different vendors. The paper will also outline how CAISO created CIM extensions for different market and grid applications and network models used by CAISO. Index Terms-Common Information Model (CIM), California Independent System Operator Corporation (CAISO), Full Network Model, Market CIM Extension