Impedance spectroscopy is a widespread technique applied in the characterization of fuel cells. The use of appropriate electrical models allows accessing fundamental information of physic-chemical processes governing the response of these devices. In this work we will review the models applied in the analysis of a variety of photoelectrochemical and fuel cells and the interpretation the different resistances and capacitances typically employed in the equivalent circuits used to fit experimental impedance data. The relationship between current-voltage curves and impedance data will be also explained.