Bonnet polishing (BP) is a flexible ultra-precision machining technique widely applied in the fabrication of optical components, especially for freeform and aspheric surfaces requiring nanometric surface quality and sub-micrometer form accuracy. Owing to its localized and controllable material removal mechanism, BP is well-suited for corrective and conformal polishing tasks. This chapter provides a comprehensive overview of the fundamental principles of BP, including tool influence functions, material removal modeling, and key process parameters. Both finite element and numerical methods are used to analyze the effects of tool kinematics on removal performance. Typical application scenarios, surface quality outcomes, and current challenges such as edge effects and mid-spatial frequency errors are discussed, offering insights into the optimization and advancement of BP technology.