Ion beam polishing (IBP) is the highest precision manufacturing technology widely applied in optical, semiconductor, and other fields. This chapter systematically introduces the theoretical foundations, process mechanisms, and practical implementations of IBP. First, the material removal mechanism based on ion sputtering theory is introduced, including microplastic behavior modeling and material removal predictions under ion bombardment. The deterministic IBP theory is then elaborated, encompassing the ion beam removal function, dwell time algorithms for surface error correction, and the development of processing equipment. Practical examples demonstrate the effectiveness of IBP in achieving sub-nanometer surface accuracy. Finally, the chapter summarizes the current state of IBP technology and prospects for future directions, such as enhancing multiphase sputtering models, advancing multiscale surface evolution simulations, and expanding applications in ultra-smooth manufacturing of complex materials. This work provides a comprehensive reference for optimizing IBF processes and advancing high-precision surface fabrication technologies.