Energy storage systems enable efficient and sustainable use of renewable energy sources and generally ensure optimal energy use. They are used for load balancing, contribute to the security of energy supply in the liberalized energy market, provide peak power, and enable a mobile energy supply. Contents: - Air as a storage medium - Hydrogen as an energy carrier and its storage - Gaseous hydrocarbons and their storage - Storage of liquid and solid energy carriers - Thermal energy storage - Storage and pumped storage power plants - Springs as energy storage - Flywheel storage - Electrochemical energy storage - Energy storage with capacitors - Superconducting magnetic energy storage (SMES).