Oxidation usually dominates high-temperature corrosion reactions, but under certain conditions, some alloys may be affected by nitridation as well. This chapter explains why nitridation occurs and how it attacks various metals, in some cases, penetrating deeper than oxidation. It provides images and data describing the nitridation process and its effects on metals and alloys in high-temperature air as well as NH3-H2O, NH3 and H2-N2-NH3, and N2 environments. It also includes test data showing that nitridation is more severe in a nitrogen atmosphere than an ammonia environment at 1090 °C (2000 °F).