This book discusses the needs of future energy systems with a focus on the electricity and transportation sectors. The general idea behind electricity based fuel is explained, the current status and future potential developments of this technology are presented. A main challenge in the production of electricity based fuels is the fluctuating energy input from renewable electricity generation. The arising design and optimization targets for integrated power-to-fuel plants are discussed, also presenting plant design and operation strategies. The book gives an outlook on future expected production costs of electricity based fuels and compares it with fossil fuels and alternatives.