The rapid expansion of variable renewable energy sources such as wind and solar has introduced significant challenges to power grid stability, flexibility, and reliability. Energy storage technologies are therefore essential to enable large-scale renewable integration and deep decarbonization of electricity systems. Among the available options, hydrogen-based energy storage has emerged as a promising long-duration and seasonal storage solution due to its high energy density, scalability, and cross-sector coupling potential. This chapter examines the role of hydrogen as an energy carrier within modern power grids, focusing on power-to-hydrogen-to-power pathways enabled by electrolysis, hydrogen storage, and reconversion through fuel cells or hydrogen-fueled turbines. Key technological components, system architectures, and integration strategies are critically reviewed, along with operational, economic, and infrastructure-related challenges. The chapter further explores the contribution of hydrogen-based storage to grid flexibility, renewable curtailment reduction, and emissions mitigation, highlighting its synergies with transportation, industry, and heating sectors. Policy frameworks, market mechanisms, and future research directions necessary for large-scale deployment are also discussed. Overall, hydrogen-based energy storage is presented as a pivotal enabler for achieving resilient, low-carbon power systems and advancing the global transition toward sustainable energy futures.