Energy storage mediums are matter that store some form of energy that can be drawn upon at a later time to perform some useful operation. A device that stores energy is sometimes called an accumulator. All forms of energy are either potential energy. As Energy storage technology may be applied to a number of areas that differ in power and energy requirements, there is a need to perform research and development on a wide variety of storage technologies. Enhanced energy storage can provide multiple benefits to both power industry and its customers. The subject areas of energy storage also seek to improve energy storage density by conducting research into advanced electrolytes and nanostructured electrodes. The goal of world-wide energy storage programmes is to develop advanced energy storage technologies and systems, in collaboration with industry, to increase the reliability, performance and competitiveness of electric generation, transmission and use in utility tied and off-grid systems. This book is a reference book on the subject. It provides a brief introduction to energy science and technology with focus on energy units, energy density, energy science and technology. The issues and processes related to power supply, power transmission, power source, electricity generation and retailing are analysed. This book also covers the subject areas of magnetic energy storage, natural gas storage and energy storage systems.