Abstract10.1 Introduction10.2 Cell reactions, general features, and operating principles10.3 Cell materials10.4 Electrolyte preparation and optimization10.5 Cell and battery performance10.6 State-of-charge (SOC) monitoring and flow rate control10.7 Field trials, demonstrations, and commercialization10.8 Other VRB chemistries10.9 Modeling and simulations10.10 Cost considerations10.11 Conclusions