Fuel cells have been applied for practical power generation in spacecraft since the first manned flight. Because of their wide range of potentially attractive characteristics and supported by the oil shocks of the 1970s as well as growing environmental concerns, their development for terrestrial applications has been pursued ever since. Today the first wide-spread demonstrations are taking place. This paper will give a review of the principles, characteristics, construction, system lay-outs and development status of fuel cells. The prospects for integration in energy supply infrastructures and further commercialisation will be discussed.