This chapter examines various energy and fuel storage technologies. The energy storage technologies include batteries, capacitors and supercapacitors, mechanical energy storage systems like compressed air and flywheels, thermal energy storage systems like phase change and thermochemical storage systems, molten salt thermal energy storage plants, storage tanks with modular heat batteries and geothermal heat storage systems, and finally modular pumped hydropower energy storage systems. The chapter examines in great detail the use of modular systems for all these different types of energy storage systems. The chapter also examines modular storage for liquid fuel, hydrogen, compressed natural gas, and liquefied natural gas. For hydrogen, the use of hydrides is very prominent. Modular CNG tanks are used globally. The future of modular LNG tanks is very bright. Membrane modular LNG tank and vacuum-insulated LNG tanks are becoming more popular as the use of LNG for power plants is globally increasing.