In this book, the transient characteristics of the grounding systems are reviewed. The concepts, advantages, and disadvantages of the existing grounding system models (electromagnetic, circuit, hybrid, and transmission line) are critically reviewed. Next, the factors, which affect the accuracy of the grounding system, namely, the effect of current-rate-of rise, and the soil ionization are investigated. Further, the effects of both factors on the voltage response of the grounding electrode are analyzed. Finally, the well-known soil ionization models are critically reviewed. The concepts, advantages, and disadvantages of the soil ionization models are reviewed. The accuracy of the soil ionization models is evaluated by comparing the electrode resistance and electrode voltage response obtained by computation with those obtained by experiment.