A critical discussion of an emerging nuclear technology -accelerator-driven subcritical systems (ADSS) for nuclear transmutations is the subject of this paper. Starting from a general background of world energy problems, the perspectives of nuclear power are discussed. On this basis it is concluded that, in response to the gradual exhaustion of fossil organic fuels, nuclear energy will play a major role provided a solution is found to various obstacles (insufficient safety - hazard of super prompt criticality and radioactive waste). The ADSS technology is considered, describing first the physical preconditionings of existing critical systems Versus subcritical ones. It is indicated that in the existing systems a desirable closing of the fuel cycle is hardly possible since the minor actinides (MA) (unavoidably produced in significant quantities) show properties that for safety reasons disqualify them as fuel for critical systems. In this context, the remoteness of subcritical systems from super prompt criticality is pointed out as a parameter responsible for the key difference between the above systems. A superiority of subcritical ones is shown by comparing their behaviour in the case of a rapid reactivity insertion, that brings no risk in these, in contrast to the fast critical ones, thus giving good grounds for the development of this technology. One of the most viable forms of application of ADSS is a symbiotic nuclear energy system, consisting of an accelerator-driven unit and a number of co-operating light water reactors (LWRs). Finally, the research problems and difficulties are mentioned. It is noted that any form of closed fuel cycle cannot avoid dealing with large quantities of radioactive materials (actinides included), and their consequent problems. Yet, it seems that a definitive elimination of actinides and the use of enormous released energy are worth this price. Summarising, the concept of accelerator-driven subcritical systems for nuclear transmutations significantly heightens the safety of nuclear power systems. Since this might facilitate social acceptance and deployment of nuclear energy, this technology is a most promising emerging option. Copyright (C) 2000 John Wiley & Sons, Ltd.