Our recent investigations on the electronic structures and chemical bonding in hydrogen-storage compounds and their hydrides are reviewed in search of a new method for materials design. It is found that hydrogen interacts more strongly with hydride non-forming elements, B, (e.g., Ni, Mn, Fe) than hydride forming elements, A, (e.g., La, Zr, Ti, Mg) in every hydrogen-storage compound, despite that there is a larger affinity of A element for hydrogen than B element in the binary metal-hydrogen system. The stability of hydrides can be elucidated in terms of the nature of chemical bond between atoms in a small polyhedron where hydrogen is stored and also of the crystal structural evolution in the course of hydrogenation. In addition, it is shown that the A/B compositional ratio of hydrogen-storage compounds is predictable using a simple parameter, 2xBo(A-B)/[Bo(A-A)+Bo(B-B)], where Bo(A-B), Bo(A-A) and Bo(B-B) are the bond orders between atoms given in the parentheses. Such parameters are shown for a variety of combinations of A and B elements.