The liquid fluoride thorium reactor (acronym LFTR; often pronounced lifter) is a type of molten salt reactor. LFTRs use the thorium fuel cycle with a fluoride-based, molten, liquid salt for fuel. Molten-salt-fueled reactors (MSRs) supply the nuclear fuel in the form of a molten salt mixture. They should not be confused with molten salt-cooled high temperature reactors (fluoride high-temperature reactors, FHRs) that use a solid fuel. Molten salt reactors, as a class, include both burners and breeders in fast or thermal spectra, using fluoride or chloride salt-based fuels and a range of fissile or fertile consumables. LFTRs are defined by the use of fluoride fuel salts and the breeding of thorium into uranium-233 in the thermal spectrum. In a LFTR, thorium and uranium-233 are dissolved in carrier salts, forming a liquid fuel. In a typical operation, the liquid is pumped between a critical core and an external heat exchanger where the heat is transferred to a nonradioactive secondary salt. The secondary salt then transfers its heat to a steam turbine or closed-cycle gas turbine. This technology was first investigated at the Oak Ridge National Laboratory Molten-Salt Reactor Experiment in the 1960s. It has recently been the subject of a renewed interest worldwide. Japan, China, the UK and private US, Czech, Canadian and Australian companies have expressed intent to develop and commercialize the technology. LFTRs differ from other power reactors in almost every aspect: they use thorium rather than uranium, operate at low pressure, receive fuel by pumping without shutdown, entail no risk of nuclear meltdown, use a salt coolant and produce higher operating temperatures. These distinctive characteristics give rise to many potential advantages, as well as design challenges.