During the last century, electrical geophysics has been transformed from a simple resistivity method to a modern technology that uses complex data-acquisition systems and high-performance computers for enhanced data modeling and interpretation. Not only the methods and equipment have changed but also our ideas about the geoelectrical models used for interpretation have been modified tremendously. This paper describes the evolution of the conceptual and technical foundations of EM methods. It outlines a frame-work for further development, which should focus on multi-transmitter and multireceiver surveys, analogous to seismic data-acquisition systems. Important potential topics of future research efforts are in the areas of multidimensional model-ing and inversion, including a new approach to the formula-tion and understanding of EM fields based on flux and volt-age representation, which corresponds well to geophysical experiments involving the measurement of voltage and flux of electric and magnetic fields.
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