Cathodic plasma electrolytic oxidation (CPEO) has been employed to rapidly fabricate oxide coatings on the cathode to enhance their wear and corrosion resistance. Compared with conventional microarc oxidation (MAO) or anodic plasma electrolytic oxidation (PEO), CPEO significantly enhances the growth rate of oxide coating, making it suitable for surface modification on valve and non-valve metals. This chapter provides an overview of the basic principles of the CPEO technique, including the liquid-phase electrical discharge phenomenon, the dependence on voltage and current, the formation and breakdown of vapor-gaseous envelopes (VGE), and the near-surface temperature changes inside the cathode. Optical emission spectroscopic measurements and calculation results for plasma parameters are described, and the CPEO mechanism in VGE plasma discharge around the cathode environment is examined. Subsequently, the morphology, structure, and properties of CPEO coatings on the carbon steel, stainless steel, Mo and TiAl alloys, and the characteristics of the carbon powders suspended in the electrolytic solution are listed in this chapter. Finally, conclusions and an outlook on future development and application of CPEO technology are presented in the final section.