Fusion works. It powers the Sun and the other stars, and the Joint European Torus (JET) at Culham in the UK has produced 16 MW of fusion power. Fusion has many potential advantages, including essentially limitless fuel, no carbon dioxide or other emissions, and intrinsic safety. Recent progress has been good and the outlook is promising. Several steps are needed before a prototype (demonstration) power station ('DEMO') can be brought into operation. These steps are: (1) build a power-station-size experimental device (an international tokamak experimental reactor (ITER)) and a materials test facility (i.e. an international fusion materials irradiation facility (IFMIF)), which will take 10 years: (2) run these facilities and incorporate the results into the design of DEMO-up to a further 10 years; and (3) build DEMO-up to another 10 years. DEMO could therefore be in operation within 30 years. Fusion power could follow on a significant scale, 10 or more 1.5 GW power stations, before the middle of this century. In the second part of the century, fusion could power large centres of population and perhaps be used to produce hydrogen fuel. Meeting growing energy demand (primarily driven by needs in developing countries) while reducing carbon emissions is a large and growing challenge. A portfolio approach is needed-there is no magic bullet. Given fusion's potential, it is essential that it is developed as rapidly as is reasonably possible (even if success is not 100% certain) as one of very few options available for large-scale production of base-load power. (C) 2008 Queen's Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved.