Abstract: To fully utilize the abundant source of renewable energy, it is essential to deploy the advanced energy storage systems for addressing the inherent intermittent feature of renewable energy. All-iron redox flow batteries (AIRFBs) use iron-based active redox species in both the anolyte and catholyte, which are promising for the next-generation large-scale energy storage systems due to their abundant raw materials, low cost, environmental friendliness, manageable crossover and excellent safety of using H₂O as solvent. This review introduces the basic principles of Fe-based electrochemistry and classifies AIRFB into deposition-stripping (D−S) type and all-soluble (A−S) type systems based on the characteristics of the anode reactions. The D−S type AIRFBs use Fe²⁺/Fe⁰ negative redox and Fe²⁺/Fe³⁺ positive redox in acidic electrolytes, thus the batteries involve in metal plating/stripping during cycling. Currently, the advancement of D−S AIRFBs is hindered by hydrogen evolution reaction (HER), dendrite formation and inferior reversibility of deposition/stripping at anodes. To address these challenges, researchers have developed various strategies, such as electrolyte optimization, electrode modification, as well as flow system improvement. These strategies contribute to inhibit parasitic reactions and enhance the efficiencies of batteries. Additionally, A−S AIRFBs use alkaline/near-neutral electrolytes, and the homogeneous Fe²⁺/Fe³⁺ redox is used for both cathode and anode, which requires ligands to stabilize Fe ions for preventing precipitation. The A−S AIRFBs avoid solid phase limitations, so they can achieve the decoupling of power and energy, improving operational scalability. However, the A−S AIRFBs face challenges in the solubility and stability of anodic redox complexes. The capacity attenuation mechanisms have been explored, and new designs of ligands are introduced for solving the issues of Fe complexes. Overall, AIRFBs are in the initial development stage, and this review provides an in-depth and comprehensive advancement of AIRFBs. New strategies are expected to support the continued development of the AIRFBs, increasing the efficiency and lifespan for boosting their commercialization potential.