Reinforcement of cements with very fine fibers of carbon and steel in mono- and hybrid-forms has been investigated. While both carbon and steel fibers led to considerable improvements in strength and toughness, on a comparative basis, carbon fibers bring about a better improvement in the toughness or energy absorption, and the steel fibers impart higher tensile strengths to the base cement matrices. In the hybrid-fiber systems, the improvements lie somewhere in between those of the equivalent mono-fiber systems.