A collection totalling some 37 binary metal–hydrogen (M–H) phase diagrams, has been assembled in a recently published monograph, with 20 of these being covered in considerable detail. From insight gained in this exercise, a selection has been made of some features of particular phase diagrams, those of the Fe–H, Nb–H and V–H systems, which should be of interest for the planning of future experiments. This work has, of course, made use of traditional principles in the compilation of phase diagrams from experimental data but it has also benefited from an increased inventory of constraints which is now available for M–H systems. A summary of this enhanced capability is presented.