Compressor stability in the form of surge and stall is a major concernfor designers of compressor. Under many conditions, unstable flowconditions are initiated in the endwall flow region of a compressor. Ifaerodynamic stall in the endwall region can be delayed, the stability ofthe compressor may be improved. Over the last 30 years, various forms ofcasing treatment have been employed for improving the endwall flow andhence enhancing the compressor stability. This paper reviews theexperimental investigations, theoretical analyses and numericalinvestigations on the casing treatment of the axial-flow compressor. Thefundamental mechanisms of casing treatments and their relative effectson the compressor performance and stability are summarized. Somerecommendations are made for future researches.