Harvesting energy from intermittent and unstable renewable sources yet producing massive and stable output require large‐scale energy storage systems. Redox‐flow batteries have attracted extensive attention because of their flexibility and scalability and are promising large‐scale energy storage systems for electrical grids. As an emerging member of the redox‐flow battery family, polysulfide flow batteries exhibit a relatively high energy density with ultralow chemical cost of the redox active materials. The special solution chemistry and complex conversions between sulfur and polysulfides with long and short chains lead to various system design schemes and complicated reaction mechanisms. Here, we present a review of various polysulfide flow battery systems developed to date and their underlying reaction mechanism and offer our perspective for their future development.