Hydrothermal chemistry and hydrothermal biochemistry have now been generally accepted as effective routes to advanced materials and biologically functional systems.The reasons for utilizing hydrothermal reactions are basically based on the favorable thermodynamics and self-catalytic kinetics.Besides thermodynamically stable phases, metastable phases are readily formed for particular water medium features at certain temperatures and pressures.In addition, it is ready for controlling and tuning valence states of elements in the sealed systems and nanometer sized forms of solids in the process of hydrothermal crystallization.In hydrothermal chemistry the conventional syntheses of minerals and zeolites have been expanded to the advanced materials, such as superionic conductors, chemical sensors, electrically conducting solids, complex oxide ceramics and fluorides, magnetic materials, luminescence phosphors, ferroelectric materials, energy storage and high efficiency applicable materials,hydrogen storage and CO2 catalytic materials.In addition, hydrothermal synthesis plays an important role in biochemistry and environmental science, such as the origin of life and the supercritical water oxidation process for decomposing organic wastes.