In this paper, the mechanisms and models of alternating current (AC) corrosion are critically reviewed to provide a systematic understanding for the further development of AC corrosion theory. None of the proposed mechanisms could give a full explanation of the AC corrosion behaviors, and no technical consensus has been reached. The models were gradually modified by relaxing the assumptions to more and more realistic situations, but no new concept was introduced in the improvement. Moreover, most of the proposed models were not verified by experiments quantitatively. Therefore, AC corrosion phenomena are far from comprehensive understanding and still need further study.