 Energy storage systems, ESS, improve the efficiency and stability of electrical networks by mitigating supply intermittency and flywheel energy storage systems, FESS, offer advantages as an energy storage solution due to their high cycle life, long operational life, high round-trip efficiency, high power density, low environmental impact, and ability to store megajill levels of energy with no upper limit when configured in banks. This paper provides a critical review of FESS, including its main components and applications, and recommends future research. This article was authored by Mustafa E. Amir and Keith R. Polin.