Despite the extensive use of electrochemical impedance spectroscopy (EIS) in diagnosing proton exchange membrane fuel cells, the differences between EIS-based measurement and process models are still not clear, causing often dubious interpretations. These differences, mainly related to the approach used in obtaining the equivalent circuit, are discussed here. The procedure for obtaining the equivalent circuit from the analytical solution and the importance of such a procedure, which distinguishes the process models from other analytical models, are also outlined. In addition, the paper presents the new semi-process model category, presenting the equivalent circuit in a different way than the process models. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.