Aqueous potassium‐ion batteries have emerged as a promising energy storage technology by combining the intrinsic safety of aqueous electrolytes with the high natural abundance of potassium. However, the narrow electrochemical stability window of water and the limited availability of suitable cathode and anode materials impose critical challenges on achieving high energy density and long‐term cycling stability. In recent years, substantial progress has been achieved through electrolyte engineering strategies, which effectively suppress water activity, expand the operational voltage window, and stabilize electrode–electrolyte interfaces. On the cathode side, advances in materials such as Prussian blue analogs, transition‐metal oxides, and polyanionic compounds have significantly improved structural robustness and K diffusion kinetics. On the anode side, increasing attention has been devoted to interfacial regulation, kinetic compatibility, and mechanical stability under aqueous conditions. Importantly, emerging insights into electrolyte‐material interactions reveal that interfacial chemistry plays a decisive role in governing the reversibility and durability of aqueous potassium‐ion batteries. This review systematically summarizes recent progress in electrolytes, cathode materials, and anode materials for aqueous potassium‐ion batteries. It highlights the remaining challenges and future perspectives toward high‐energy‐density, durable, and practically viable aqueous potassium‐ion batteries.