The transition of the current energy infrastructure from fossil fuels to renewable energy sources is critical to the continuous prosperity of our society and economy.In order to accelerate the extensive adoption of the sustainable energy sources,challenges of intermittence and instability from the renewables must be resolved.Therefore,large-scale energy storage technologies,especially flow batteries,have attracted more and more attention,mainly because flow batteries own very intriguing characteristics of independently tuned power and capacity,high safety,high efficiency,long cycle life,flexible modular design,and low cost.In recent years,research and development (R&D) on various kinds of flow batteries have reported,including traditional zin(c)-bromine flow batteries (ZBFBs) and vanadium flow batteries (VFBs).Many of these possess variable attractive features and can consequently satisfy diverse users\' demands.Up to now,VFBs and other types of flow batteries have been demonstrated,such as 5 MW/10 MWh VFB system combined with a 50 MW wind farm in Faku,Shenyang.However,there are still challenges for traditional flow batteries to further expand their industrialization.Thus,many novel aqueous and organic flow battery systems have been proposed recently,such as organic-based flow batteries.In fact,for both conventional and novel flow battery systems,the improvement in their energy density and power density,along with the decrease in their cost is the ultimate aim of the R&D.In general,this aim will be accomplished mainly by designing and optimizing the key materials of flow batteries,including electrolytes,electrodes,separators,and so forth.In recent years,many significant breakthroughs and achievements in the field of flow batteries have been reported.Herein,in order to better understand and promote the R&D in the field of flow batteries,a special column titled “Flow battery” on Journal of Energy Chemistry is ensued for the interested readers.