Fans are used in many industrial, building and household applications, especially for ventilation, and are often considered as particularly noisy components. A large amount of work has been carried out for improving knowledge on fan noise generation and finding noise reduction means. These researches mainly rely on works initially performed on rotating machinery used for instance in aeronautic applications, but significant differences exist between the noise mechanisms of high speed fans of aircraft engines and those of low speed domestic or industrial fans. Furthermore, on account of the variety in the types of fans and the complexity of the internal flowfield, many unclear areas remain in the understanding and prediction of fan noise. Reference  presents a non-exhaustive state of the art of the knowledge in this field.