Fluid jet polishing (FJP) is an advanced surface finishing process that utilizes high-pressure water jets combined with abrasive particles to achieve ultra-smooth surfaces on various materials. This chapter provides an indepth exploration of the FJP process, focusing on the material removal mechanisms, the interaction between water and abrasives, and the factors that influence polishing effectiveness. Key parameters such as jet pressure, stand-off distance, abrasive type, and jet angle are examined for their impact on surface quality and precision. The chapter highlights the advantages of FJP, including good surface quality, high form maintenance ability, and the ability to process materials with complex geometries and hard-to-reach areas. Applications of FJP in industries such as microstructured surface polishing, corrective polishing of optics, and tool marks removal are discussed, showcasing its versatility in achieving high-quality finishes. Additionally, the challenges and limitations of FJP are considered, along with ongoing advancements in technology that enhance its capabilities for ultra-precision surface finishing.