In order to drive hydrogen economy, there is a need for efficient hydrogen storage materials which can store high weight percentage of hydrogen that can be absorbed/desorbed efficiently within the operable emperature and pressure. Metal hydrides have good sorption kinetics, but they have low weight percentage of hydrogen. On the other hand, complex hydrides have high weight percentage of hydrogen but they lack good kinetics. Also, the decomposition temperatures of complex hydrides are too high to use them in mobile applications. In this talk I will focus on both metal hydrides and complex hydrides. I will show how ab-initio calculation can be used to design these hydrides with desired properties and predict their properties including crystal structure. Particular attention will be paid to demonstrate how one can understand complex bonding nature of these systems using various tools, thereby understand their decomposition behaviour. I will show how theory can be used to predict site occupation of hydrogen in metal hydrides and also demonstrate the violation of the established empirical rule for short H-H distance in metal hydrides. Nanophase engineering, changes under high-pressure, and lattice dynamics of these hydrides will be discussed.