Almost every individual, organisational, and societal activity is linked to, and dependent on, the use of one or more forms of energy. The development of a nation and the quality of life of its population are closely related to the amount and types of energy consumption. In the face of an increasing world population, improving the standard of living in developing countries, and maintaining the levels that have been reached in advanced industrialised countries, will require a considerable increase in the world's use of energy. The challenge is to make this use compatible with sustainability.