Basic characteristics such as classification and crystal structure of different metal hydrides are discussed together with their thermodynamic aspects. The development of magnesium based alloys, titanium based alloys, rare earth/mischmetal intermetallic compounds and zirconium-manganese based systems is discussed along with a variety of industrial applications such as portable hydrogen containers, hydrogen powered automobiles, utility load levelling and peak shaving, reversible electrodes in rechargeable batteries, compressors and water lift pumps, thermally actuated pumps and separation of hydrogen isotopes and coal gasification product streams.