This chapter provides a systematic exposition of abrasive flow machining (AFM) principles and methodologies. It presents a comprehensive overview of the composition, preparation, and characteristics of different abrasive and analyzes their rheological behavior, surface finishing mechanisms, and process efficiency. The text further integrates modeling and simulation approaches to elucidate the underlying physics of AFM, offering quantitative insights into parameter optimization and surface quality prediction. Additionally, the monograph examines external energy field-assisted AFM techniques, notably magnetic field-assisted, and ultrasonic vibration-assisted AFM, detailing their synergistic effects in improving material removal rates and enhancing final surface integrity. Through representative applications in micro-hole processing, complex flow channel finishing, and intricate surface polishing, the versatility and industrial significance of AFM are demonstrated, particularly in aerospace, precision moldmaking, biomedical devices, and the automotive sector. The work concludes by addressing current challenges—such as process stability, media innovation, and system integration—and projecting future research avenues that may further advance the capabilities of AFM. This monograph serves as a valuable reference for researchers, graduate students, and industry professionals engaged in ultra-precision machining and advanced manufacturing.