Controlling vulnerabilities related to ageing assets, increasing climatic stress and increased utilization of components is an essential part of power system asset management. Previous studies have revealed that there is a need for new knowledge for monitoring and managing vulnerability in the electric power grids. The best available database for documenting the development of the reliability of supply is the failure and interruption statistics. However, these data only contain information about current components and those that have failed. Presently there are few, if any, indicators or data on an aggregate level to monitor and describe the vulnerabilities in quantitative terms, and to identify e.g. underlying mechanisms impacting the technical condition of the grid. This report gives an overview of the state of the art in literature for indicators to measure the vulnerability of infrastructures in general and more specifically of the power system. Gaps according to the needs of the electricity business are identified and discussed, and a common basis of the most important terms for vulnerability indicators is established. Further, a framework is described for development of electric power grid vulnerability indicators, and examples of possible indicators are presented.