Publisher Summary The hydrothermal technique is especially suitable for obtaining pure and high quality crystals of elements. This chapter describes the hydrothermal synthesis of selected native element crystals. It also describes the hydrothermal growth of selected oxides of both gemstone and technological grades. Oxides form one of the largest groups of inorganic compounds both in nature and in the laboratory. A large number of oxides obtained by the hydrothermal method: TiO2, ZrO2, HfO2, Cu2O, BeO, Bi2O3, In2O3, Al2O3, ZnO, Fe2O3, to mention a few, and a great variety of mixed oxides. The native element crystals popularly grown under hydrothermal conditions are gold, silver, platinum, copper, arsenic, cobalt, nickel, tellurium and bismuth related compounds. Similarly, among the hydrothermally produced oxides, zincite, rutile, zirconia, and hafnia are very popular. In fact, the hydrothermal method is the only suitable method for the growth of these compounds for various reasons like high melting point, very low solubility, acid resistance, and so on.