Sparking phenomena inherent to plasma electrolytic oxidation (PEO) are not fully understood yet and several sparking regimes can occur along a PEO process. In this chapter, sparking discharge regimes and the role of soft sparking are reviewed in the context of PEO. First, the important aspect of the electrolyte–material interaction is discussed based on the behaviour of charges and space charges in semiconductor–electrolyte contact from both electrolyte and semiconductor points of view. The oxide film formation, its stability, and breakdown phenomena are reviewed. The type and mode of electrical discharge used in PEO are introduced by distinguishing DC voltage and current, AC, unipolar-pulsed and bipolar-pulsed regimes. Recent strategies to optimize the quality of the layers and minimize energy consumption are discussed. General features related to the promising soft sparking mode are reviewed, and the influence of some main process parameters on the transition to soft regime is presented. The concept of active zone is briefly exposed to illustrate the mechanisms at the interfaces, which support the soft sparking regime. Finally, new strategies involving the soft sparking regime are discussed. These involve the use of pre-anodized samples or cold-spray treatments prior to PEO, or the incorporation of micro- or nano-particles in the PEO layers.