AbstractFusion reactors have inherent safety advantages, but also have sources of potential hazards to cause undue radiation exposure to the public and site personnel if the reliability of engineered measures is not adequate. In order to avoid realization of potential hazards of nuclear facilities, the safety regulation of design, construction and operation is implemented through governmental licenses. The International Thermonuclear Experimental Reactor, whose engineering design activity is ongoing will be the first challenge to demonstrating licensable fusion reactor safety. From the view point of licensable safety, this paper reviews prospective safety principles, safety requirements, issues in ensuring reliability and necessary research and development for fusion reactors.