Large electrical generating stations are not built in a day; 6 to 20 years might elapse between the decision to build and the satisfactory operation of a station. The C.E.G.B. has tried to ensure that enough generating capacity is available to avoid ‘power-cuts’ at all seasons and this brief account explains the hazards, the failures and the successes of the forecasts which have had to be made over the years. There have been many available options for the generation of electricity and the way ahead for the last decades of the Century is forecast.