Recent theoretical results concerning mechanisms for mass-transport-limited electrochemical polishing are summarized and discussed. The underlying physical bases for both salt-film and acceptor models are presented with particular emphasis on the differences in their alternating-current impedance behavior. Direct comparison of the dependence on operating conditions of characteristic features of the impedance diagrams in the high-frequency range provides a clear experimental basis to distinguish among the various mechanisms that can lead to the polishing phenomenon in specific cases.