This paper describes how to begin with extensive geoelectric measurements of an aquifer along with a few hydraulic measurements and end with an estimate of the aquifer's hydraulic conductivity field and spectrum at variable scales. It is based on a preponderance of theoretical and empirical evidence indicating that electrical and hydraulic (eh) conductivities of aquifers are linearly correlated on a bilogarithmic scale. The steps required for a geoelectric characterization are scaling up, calibration, and spectrum estimation. Scaling up estimates electrical conductivity at variable scales from the apparent resistivity measurement. Calibration equilibrates coincident, equal-scale eh conductivities using the theoretical eh conductivity correlation. Combined, scaling up and calibration provide a variable-scale expression for the hydraulic conductivity field in terms of a geoelectric measurement. From this expression the hydraulic conductivity field spectrum is calculated. These steps are applied to borehole data collected at the Department of Energy Central Nevada Testing Area and the U.S. Geological Survey Cape Cod site. In each case a statistically significant eh conductivity correlation is observed. The paper ends by conjecturing that a horizontal exploitation of the eh conductivity correlation offers for the first time an inexpensive means of characterizing the hydraulic conductivity field at a high resolution and over a large area. ¿ 2000 American Geophysical Union