The current energy storage system technologies are undergoing a historic transformation to become more sustainable and dynamic. Beyond the traditional applications of battery energy storage systems (BESSs), they have also emerged as a promising solution for some major operational and planning challenges of modern power systems and microgrids, for example, enabling the integration of renewable energy sources by reducing their intermittency and improving the voltage, frequency, and reliability profiles of power grids. In other words, energy arbitrage, increased capacity of renewable energy resources, deferred investment in power grid components, reduced congestions, reduced carbon footprint, reduced losses, and stability stress the importance of conducting extensive and ground-breaking research and experimentation in the area of BESSs. This effort will maximize the benefits of using existing and novel BESS technologies in power systems. However, the success in the use of BESSs is driven by many technological developments and cost reductions. The current special issue enables a unique, dedicated opportunity to disseminate state-of-the-art research works in innovative aspects of BESSs from the technology and system points of view.