Energy storage systems (ESSs) are the technologies that have driven our society to an extent where the management of the electrical network is easily feasible. The balance in supply-demand, stability, voltage and frequency lag control, and improvement in power quality are the significant attributes that fascinate the world toward the ESS technology. However, being one of the oldest ESS, the flywheel ESS (FESS) has acquired the tendency to raise itself among others being eco-friendly and storing energy up to megajoule (MJ). Along with these, FESS also surpasses the quality of high power density, longer life cycle, higher rate of charge and discharge cycle, and greater efficiency. In this article, an overview of the FESS has been discussed concerning its background theory, structure with its associated components, characteristics, applications, cost model, control approach, stability