The United Kingdom grows a little more than one half of its food and it is shown that agriculture uses 4% of national energy to make this unprocessed food available at the farm gate. Small though this may be, it is absolutely vital to British agriculture, for present levels of productivity are highly dependent on its use, principally through the media of mechanization and fertilizers. The prospects for the United Kingdom's indigenous energy supplies are examined and it is shown that while self-sufficiency seems assured in the 1980s, before the turn of the century we may once again be competing in world markets for scarce and expensive fossil fuels. The prospects for making better use of existing and alternative energy sources in agriculture are discussed. It is shown that conservation measures may be practised in relation to existing energy sources in respect of powered machines, cultivations, drying of crops and glasshouse heating and that there are also possibilities in respect of fertilizers. New and under-used sources considered include solar energy by direct and photosynthetic means (energy crops), crop residues, animal wastes, wind power, industrial waste heat, and geothermal energy, and some examples are given of their application to agricultural systems. Some of these new and under-used sources of energy appear to offer some prospects of supplementing present sources but their future will be critically dependent on the availability and cost of energy from these more conventional sources.