Dual Fluid Reactor (DFR) is a new concept of high-temperature nuclear reactors based on fast neutrons. The name reflects the fact that liquid fuel and liquid coolant circulate two separate loops, which is a new idea in contrast to other known concepts of reactors based on some liquiid fuel (e.g. Molten-Salt Fast Reactor). Two independent loops allow to independently optimize operational parameters of fuel and coolant. A high power density and small core may result. This in turn makes feasible more expensive constructional materials, better resistant to corrosion at high temperatures.