Flywheel energy storage systems (FESSs) have been investigated in many industrial applications, ranging from conventional industries to renewables, for stationary emergency energy supply and for the delivery of high energy rates in a short time period. FESSs can be used for industrial applications ranging from aerospace stations and railway trains to electric vehicles (EVs). They have their own individual advantages and disadvantages, leading them to have their own unique roles for energy storage applications. Compared to the limitation of an electrochemical battery imposed by its inherent features, such as low power density, short duration of service, limited charge-discharge cycles and being environmentally unfriendly, FESSs exhibit some distinctive merits, such as high energy density, low cost, high reliability, high dynamics, long lifetime, high efficiency, environmental friendliness and easy monitoring of the state of charge. In this chapter, FESSs applied in EVs are discussed, with an emphasis on those operating at speeds over 10,000 rpm. The organization of this chapter is as follows. In section 3.1, a brief introduction of FESSs is presented. In section 3.2, the configuration of an FESS, including a flywheel, a motor/generator, a bearing, a power converter and an enclosure, is described. Then, in section 3.3, possible candidates for ultrahigh-speed motors/generators for FESSs are reviewed. Lastly, in section 3.4, control strategies for motor/generator control, flywheel control and power flow control are discussed.