A philosophy for electrochemical impedance spectroscopy is presented which integrates experimental observation, model development, and error analysis. This approach is differentiated from the usual sequential model development for given impedance spectra by its emphasis on obtaining supporting observations to guide model selection, use of error analysis to guide regression strategies and experimental design, and use of models to guide selection of new experiments. These concepts arc illustrated with two examples taken from the literature. This work illustrates that selection of models, even those based on physical principles, requires both error analysis and additional experimental verification. (c) 2007 Elsevier Ltd. All rights reserved.