The hydrothermal technique is very useful for growing crystals of native elements and simple 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. In this chapter, we describe the hydrothermal synthesis of selected native element crystals. Keywords polymorphism; diamond synthesis; growth kinetics; Chemical Vapor Deposition; wide band gap semiconductor; penta-antimonites; ferromagnetic