In the 1970s, many works have been published concerning potential decay measurements and interpretation (most often was the insulating sample charged by a corona discharge device, using a grid to control the charging potential). The marketing of reliable and comparatively inexpensive electrostatic probes, especially vibrating reed models, which provide a minimum surface disturbance by maintaining zero field on it, had facilitated this kind of measurements; besides, studies on polymeric films had awakened theoreticians interest, by revealing a puzzling phenomenon, the potential decay curves cross-over. Since then, development of new space charge investigation techniques, such as the pressure pulse, piezoelectroacoustic, thermal wave, or mirror method, have somewhat overshadowed this technique, by offering the great advantage to give an image of the internal space charge profile, bringing thus the “depth” dimension that potential decay models only tried to calculate from the V(t) curves shape. However, surface potential measurements by means of classical electrostatic probes still keep a place in the material characterization technique tool set. In fact, they remain the only simple and unexpensive means to investigate the charge flow in a structure with one side which cannot be metallized without obliterating the phenomenon to study. Most of the potential decay modelizations have been developed within three large fields: electrets development, adjustment of reprography devices using photoelectric activation of the conduction, and studies on polyethylene films behavior under stress, aiming at the use of this material for energy transport cables insulation. Nevertheless, one can mention numerous other applications where surface potential measurements continue to be indispensable: studies of charge flow within the electrostatic risk control framework, surface conductivity measurements on aged insulators, very low frequency material dielectric characterization, etc