This chapter addresses the hydrometallurgical processes employed to recycle lithium-ion batteries, focusing on nickel–manganese–cobalt and lithium–iron phosphate chemistries. It begins by discussing the mechanical pretreatment steps to liberate the various battery components. Pyrometallurgical methods are briefly covered, but the emphasis is on hydrometallurgical techniques, which are increasingly relied upon in the industry. The leaching process is examined in detail, including the use of inorganic and organic acids, as well as ammonia-based solutions. Oxidative precipitation, liquid–liquid extraction, and crystallization-precipitation are then explored as downstream purification and separation steps. Emerging innovations are also reviewed, such as thermal treatments, mechanochemical processing, advanced liquid–liquid extraction, electrodialysis, and novel crystallization techniques. The production of battery-grade metal salts is highlighted, and the importance of managing impurities to meet strict specifications for cathode active material synthesis is discussed. Finally, the chapter provides an overview of the Li-cycle recycling process as an industry example.