The mechanisms underlying compressor noise radiation are reviewed in detail with particular emphasis on potential methods for compressor noise reduction. It appears that many independent methods of reducing compressor noise are possible, so that large (20–30 dB) reductions of noise radiation may be practicable. Analyses of the effects of rotor-stator spacing and duct-mode directivity are presented. It is concluded that an increase in the number of rotor blades may be desirable from several points of view.