Among the different possible solutions for the reduction of greenhouse effect, hydrogen has been proposed as a clean and efficient energy carrier. However, high capacity storage is still to be developed. Many metals, alloys and intermetallic compounds are able to store hydrogen gas. Such possibility is of interest in terms of safety, global yield and long time storage. However, to be suitable for applications, such compounds must present high capacity, good reversibility, fast reactivity and sustainability. In this paper, we will review on the thermodynamic properties of metal hydrides. Their solid-gas hydrogenation behaviour and the related absorption-desorption isotherm curves are examined as a useful criterion for the selection of suitable materials for applications. The paper emphasizes the possibility to reach given properties by convenient chemical substitutions of the compounds.