ThisCarbon material chapter introduces possible interaction of hydrogen (H) with carbonCarbon (C) or graphiteGraphite, and metal carbidesCarbide in steels, aiming to help the understanding of the role of carbonCarbon in steels in its interaction with H. C is always included in steels as carbidesCarbide (either ironIron carbide carbideCarbide, or with other elements included in steels), graphite or hydrocarbonHydrocarbon. It is well known that some carbidesCarbide such as TiC, and NbC trap H most likely as carbohydrides, while H hardly interacts with graphiteGraphite at medium or lower temperatures. In contrast, the interaction of H with the graphite in steels is not understood well. Possible H trappingTrapping, at graphite, metals carbidesCarbide, and solid-phase hydrocarbonHydrocarbon in steels are discussed.