Exchange of event information among multiple interconnected power system operators has become imperative for integrated and secure operation of the system. Considerable literature is reported on the standardization of power system data, while limited work has been done on the standardization of events. In this paper, we define a high level event ontology for power systems comprising seven concepts, namely, event, event extractor, event consumer, time, measurement, location, and level. These concepts are then developed with details extracted from the operating procedures followed by national and regional load dispatch centers in the Indian national grid. The methodology adopted for designing concrete sub-ontologies from the high level event ontology is also reported. The proposed event ontology has wide applications in the areas of i) event driven architecture (EDA) which facilitates the integration of event driven applications within and across the utilities, and ii) complex event processing (CEP) which facilitates development of sense-and-respond software capable of processing events extracted from large volumes of real-time data streams. © 2011 IEEE.