Nowadays, with the large-scale penetration of distributed and renewable energy resources, ES (energy storage) stands out for its ability of adding flexibility, controlling intermittence and providing back-up generation to electrical networks. It represents the critical link between the energy supply and demand chains, being a key element for increasing the role and attractiveness of renewable generation into the power grid, providing also numerous technical and economic benefits to the power system stakeholders. On islanded systems and micro-grids, being updated about the state-of-the-art of ES systems and their benefits becomes even more relevant. Hence, in the present paper a comprehensive study and analysis of ES leading technologies' main assets, research issues, global market figures, economic benefits and technical applications is provided. Special emphasis is given to ES on islands, as a new contribution to earlier studies, addressing their particular requirements, the most appropriate technologies and existing operating projects throughout the world. •Energy storage is a key element for increasing the role and attractiveness of renewable generation.•Numerous technical and economic benefits to the power system stakeholders can be provided.•A comprehensive study and analysis of energy storage leading technologies' is presented.•Special emphasis is given to energy storage on islands, as a new contribution to earlier studies.