In the last 5 years, there has been a rapid growth in interest in the use of high-temperature (700 to 1000°C) molten and liquid fluoride salts as coolants and for other functions in nuclear systems. This interest is a consequence of new applications for high-temperature heat and the development of new reactor concepts. These salts have melting points between 350 and 500oC; thus, they are of use only in high-temperature systems. Nitrate salts with a peak operating temperature of ~600°C are the highest-temperature commercial liquid coolant available today; thus, the development of higher-temperature fluoride salts as coolants opens new nuclear and non-nuclear applications. These salts are being considered for intermediate heat transport loops between all types of hightemperature reactors (helium and salt cooled) and hydrogen production systems, oil refineries, and shale oil processing facilities. Historically, steam cycles with temperature limits of ~550°C have been the only efficient method to convert heat to electricity. This limitation produced few incentives to develop high-temperature reactors for electricity production. However, recent advances in Brayton gas-turbine technology now make it possible to convert higher-temperature heat efficiently into electricity and thus have created the enabling technology for more efficient cost-effective high-temperature reactors. The near-term advanced high-temperature reactor (AHTR) uses a graphite-matrix coated-particle fuel and a liquid salt coolant. There is the longer-term potential of a liquid-salt-cooled fast reactor (LSFR) that uses metal-clad fuel and a liquid salt coolant. The molten salt reactor (MSR), with the fuel dissolved in the molten salt coolant, is receiving increased attention because of (1) the advancing salt-coolant technology and Brayton cycles that improve the economics, (2) advances in salt chemistry that enable the development of fast-spectrum MSRs with the safety advantages of large negative void coefficients, and (3) the interest in actinide burning where MSRs avoid the need to fabricate fuel of highly active actinides. Last, there is a developing interest in liquid-wall fusion machines with much higher power densities than solid-wall fusion machines.