Redox Flow Batteries were initially developed by NASA in the 70s for its space programme. The expiry of a number of patents related to RFBs in 2006 has sparked an industrial race to commercialisation, which will grow to become a $4bn market by 2027.Often perceived as an underdog, redox flow batteries (RFB) may not deliver the same power of a Li-ion battery, but they can compete in terms of cycle life, safety, and reliability for stationary applications. Utilities around the world are avidly testing RFBs in pilot projects, while China is underway in the construction of the largest battery in the world (200 MW / 800 MWh), which will be entirely powered by redox flow batteries. If successful, this project will be replicated across the country and probably also in Europe and the US.In this report, technology analyst Dr. Lorenzo Grande from IDTechEx analyses the different flow battery chemistries available from a technology standpoint (all-vanadium, all-iron, zinc/bromine, hydrogen/bromine, polysulphide, etc.) as well as by engaging with the worlds main stakeholders (UET, Sumitomo, Primus Power, Gildemeister - just to name a few). Overall, 19 companies are included in this report, covering the whole RFB spectrum as well as all the main markets, namely USA, Europe, and Asia. The companies are compared in terms of their target markets and a series of case studies explains who are the most likely winners and why.