Carbon is an essential material in a future hydrogen energy society. In particular we focus on the roles of carbon as components of PEFCs (polymer electrolyte fuel cells). Carbon materials are used in almost all parts of a PEFC except for the electrolyte membrane. Although classical graphite and carbon black are still used, alternative carbon materials, such as nanotubes, nanofibers, graphene, and mesoporous carbon, have been developed for the purpose of increasing the activity and durability of PEFC. In this paper, the roles of carbon in separators, gas diffusion layers, and electrocatalyts of PEFC are introduced. Regarding electrocatalysts, other than their original role as catalyst supports, carbon materials work as catalysts after doping with heteroatoms. Recent research directions are also discussed.