The Super-Critical Water-cooled Reactor (SCWR) is a high temperature, high-pressure water-cooled reactor that operates above the thermodynamic critical point (374°C, 22.1MPa). The main improvement in the SCWR is in the area of economics due to the high thermal efficiency and simplifications that result from the use of supercritical (SC) water as coolant. Furthermore, the safety characteristics of the SCWR have also been advanced by the introduction of additional passive safety systems. Two reactor concepts are being considered for the SCWR including the pressure-vessel type and pressure-tube type. In addition to the primary circuit differences, thermal, fast and mixed spectra are all possible in the SCWR design. In this chapter, the various SCWR designs proposed in different countries are briefly introduced covering the core design, fuel assembly, safety systems and so on. The improvements in economics, sustainability, safety and proliferation resistance for SCWRs are analyzed as well as the challenges.