Worldwide consumption of electricity has increased steadily during the second half of the 20th century, in the developed and developing countries alike. At present, 40% of the primary energy in the world is used to generate electricity, and 14% of the energy consumed is in the form of electricity. It is expected that the consumption of electricity will continue to increase during the 21st century. During the middle part of the 20th century, coal and hydroenergy contributed 80% of the primary energy for the generation of electricity. By the start of the 21st century, coal had, in part, been replaced by oil, nuclear energy, and particularly by natural gas, which had become the preferred fuel for new power plants. However, coal remained the main source of energy for the generation of electricity. During the last two decades of the 20th century, the shares of oil and hydroenergy decreased, whereas that of nuclear energy, after rapidly increasing in the 1970s and 1980s, stabilized during the 1990s. Other sources of energy made only small contributions to the generation of electricity. During the first half of the 21st century, it is likely that coal, natural gas, and hydroenergy will be the main sources of primary energy for electricity generation. The share of coal will probably decrease, whereas that of natural gas will substantially increase. The share of oil and nuclear energy will decrease. Other sources of energy, with the possible exception of wind, will remain minor contributors. During the second half of the century, nuclear power may make a comeback, and coal and natural gas will be the main fuel for electricity generation. Oil and wind probably will make small contributions. Hydrogen may enter the electricity-generation field if some of the obstacles to its use can be eliminated.