The hardness and stress of amorphous carbon films prepared by glow discharge and by ion beam assisting deposition are investigated. Relatively hard and almost stress free amorphous carbon films were deposited by the glow discharge technique. On the other hand, by using the ion beam assisting deposition, hard films were also obtained with a stress of the same order of those found in tetrahedral amorphous carbon films. A structural analysis indicates that all films are composed of a sp²-rich network. These results contradict the currently accepted concept that both stress and hardness are only related to the concentration of sp³ sites. Furthermore, the same results also indicate that the sp² sites may also contribute to the hardness of the films.