The impact of energy storage is far-reaching, as not only does it address the issues that have limited renewable energy’s penetration, it fundamentally alters the longstanding relationship between utilities and their customers. The disruptive potential of storage is unlike other energy technologies in that it pervasively extends across the value chain in a way that stakeholders will impact and be impacted by its adoption. Energy storage can play an important role in the present, in the short-term and in the medium- term future energy scenario. Both stationary and automotive applications will be considered and the main features required by each of them for an energy storage system will be explained. A very brief description of the proven and most promising storage technologies will be given with the aim of providing an overview of the peculiarities of each one and consequently its better-suited applications. Finally, the state-of-the-art, the opportunities and the barriers to the spread of energy storage systems will be summarized.