Today’s unresolved issues in impedance spectroscopy are driven by the observation that impedance spectroscopy provides only an indirect characterization of a given system. A consequence of the inferential character of impedance spectroscopy is that many models can provide fits that fall within the apparent confidence limits of the data. Therefore impedance spectroscopy cannot be regarded as being a "stand-alone" technique. The non-uniqueness of impedance models is currently being addressed by incorporating independent in-situ and ex-situ analyses into impedance experiments, by varying addition parameters (or forcing functions) such as temperature, mass transfer rates, energy of incident monchromatic illumination and intensity of broad-band illumination, and by incorporating measurements of additional properties such as mass. Improvements in interpretation will also be driven by incorporation of more sophisticated statistical treatment of data and models.