At present approximately 85% of energy consumption is met by burning fossil fuels. The world population is at present 5.5 billion. United Nations projections for 2060 give a median prediction of population doubling, a 'worst case' prediction of tripling and a 'best possible' 50% increase. Clearly the demand for energy is likely to increase by factors of 1.5 to 10 depending on the actual population growth and the achieved improvements, if any, in the mean standard of living. Fossil fuels are a finite resource and estimated reserves correspond at present energy consumption rates to approximately 50 years for oil and gas and several hundred years for coal. The only major alternatives to fossil fuels are solar, fission and fusion power. These are all at different states of development and have very different environmental effects and perceived safety aspects. Given the magnitude of the long-term energy problem it is clearly important to aim at diversity of supply and to develop each system to its full potential. The purpose of fusion research is therefore to explore the related science and technology and to develop prototype power-generation systems.