[en] Meeting the demand of energy, also growing in the future by burning fossile fuels, becomes more and more difficult. There are raising limits in the availability and in the cost of such fuels. The only real way consists in using nuclear energy such as for the generation of electricity as for the heat supply and other purposes. Enlarging the field of nuclear energy besides that of electricity may be considerably stimulated by the gas-cooled high temperature reactor. But the crucial problem of the development of nuclear energetics is that of a long-time stable and economic supply with fissile material. This problem may only be solved by the fast breeder reactor. The current standard and future problems of the development of liquid metal cooled fast reactors are discussed. A short view on the gas-cooled fast reactors is also given. (author)