Within all electrophotographic (or xerographic) copiers and laser printers are development systems where the image is reproduced. Usually these development systems contain 200 μm diameter metallic, magnetic balls called carrier particles. Attached electrostatically to these balls are 10μm diameter polymer particles called toner which eventually end up on the paper forming the black images given to customers. The process bywhich the toner leaves the carrier and ends up on the paper is driven by electric fieldsin the development system. These fields are determined by the applied voltage and the dielectric properties of the granular mixture of metal carrier balls, polymeric toner, andair. The average electric field is determined by the dielectric constant of this granular mixture. But on a microscopic scale that a toner would experience, i.e. 10 μm, the electric field has significant structure. This structure has been determined both experimentally and theoretically. For example, the electric field peaks underneath a chainof carrier particles (which are chained up by a magnetic field). Models of the development process clearly indicate that toner particles transfer from the carrier particles only when the toner particles are directly under a carrier chain, where one would expect the field to be a maximum. However, recently we have succeeded in showing experimentally that the value of the electric field that the toner particles experience is the average field, described by the dielectric constant. Theoretical questions concerning the calculation of the electric field in a granular system raised by this unexpected result will bediscussed.