This chapter begins with an overview of the history of ion nitriding. This is followed by sections that describe how the ion nitriding process works, glow discharge characteristics, process parameters requiring good control, and the applications of plasma processing. The chapter explores what happens in the ion nitriding process and provides information on its gas ratios. It describes the reactions that occur at the surface of the material being treated during iron nitriding and defines corner effect and nitride networking. Further, the chapter provides information on the stability of surface layers and processes involved in the degradation of surface finish and control of the compound zone formation. Gases primarily used for ion nitriding and the control parameters used in ion nitriding are also covered. The chapter also presents the philosophies and advantages of the plasma generation technique for nitriding. It concludes with processes involved in oxynitriding.