Tungsten diselenide (WSe2) has a hexagonal structure consisting of single sandwiched Se and W layers with thickness of about 3.3 . WSe2 is a semiconductor with a band gap in the range of 1.2 eV - 2eV, depending on how the nonstoichiometry differs from the ideal W: Se ratio of 1:2, WSe2 is a black or gray odorless material, has good thermal stability and a high melting point. Because of its high optical absorption in the visible range, the layered arrangement between the cations, the high resistance against photocorrosion, and the magnitude of its band gap, WSe2 is an important material in photoelectrochemical energy conversion devices such as photovoltaic solar cells. WSe2 also play an important role in a number of technologies such as high temperature solid lubricants and rechargeable batteries. Very recently ultra low thermal conductivity has been reported in disordered, layered WSe2 crystals. The book is useful for everyone who works with crystal growth and its properties. In this book authors nicely present the crystal growth techniques and its various properties.