Storing energy is one of the most important challenges of our time. Energy storage systems are not only essential for switching to renewable energy sources, but also for all mobile applications. Electro-mechanical flywheel energy storage systems (FESS) can be used in hybrid vehicles as an alternative to chemical batteries or capacitors and have enormous development potential. In the first part of the book, the Supersystem Analysis, FESS is placed in a global context using a holistic approach. External influences such as the vehicle, driver and operating strategy, including socio-psychological aspects, are analyzed with regard to their interaction with the memory. From this, optimal application scenarios are derived and the development goals relevant for market success are defined. In the second part, the consideration of the subsystem, those critical components in the FESS are identified which are responsible for the achievement of the technical target properties. From the point of view of maximum cost reduction, specific solutions for the design of the key components are presented and their suitability is validated through empirical studies on the housing, bearing and rotor as well as through overall prototypes.This book is a translation of the original German 1st edition Schwungradspeicher in der Fahrzeugtechnik by Armin Buchroithner published by Springer Fachmedien Wiesbaden GmbH, part of Springer Nature in 2019.