This chapter reviews studies dealing with the characterization of the plant root system by the electrical impedance method, i.e., with resistance and capacitance at a single frequency or at multifrequencies, according to the approach used in electrical impedance spectroscopy (EIS). Several studies have shown a correlation between electrical capacitance and resistance at a single low frequency with root biomass and morphology (e.g., surface area). It has not been possible to define clearly which part of the root system the electrical parameters represent. The circuitry in the stem–root–soil continuum has been analyzed in more detail by means of EIS. Using this approach, lumped and distributed models have been formulated that consider the role of roots in the context of other components in the circuitry. By means of EIS, a parameter referring to root capacitance was found to correlate positively with root biomass and root surface area. Several open questions remain with regard to the applications of the method. More studies are needed for the evaluation of longitudinal and radial electric field distribution between root interior and soil along the root system from root collar to root tips. In addition, further studies are needed under standardized measurement conditions with soils of different ionic composition and texture as the growing substrate, and also by taking into account the role played by mycorrhizas.