Whereas the 19th century was the century of the steam engine and the 20th century was the century of the internal combustion engine, it is likely that the 21st century will be the century of the fuel cell. Full cells are now on the verge of being introduced commercially, revolutionising the way we presently produce power. Fuel cells can use hydrogen as a fuel, offering the prospect of supplying the world with clean, sustainable electrical power. The article discusses the history of fuel cells, fuel cells for NASA, alkaline fuel cells for terrestrial applications and PEM fuel cells. Fuel cell applications in transportation, distributed power generation, residential and portable power are discussed. The science of the PEM fuel cell and the direct methanol fuel cell are discussed. Benefits of fuel cells and obstacles to their widespread introduction are briefly outlined.