Owing to the absence of single crystals, powder diffraction has become a routine tool for ab-initio structure determinations of metal hydrides in our laboratory. During the past few years some 15 new structure types of complex ternary and quaternary transition metal hydrides and ternary alkaline earth hydrides have been characterised. The diffraction data were collected on X-ray, synchrotron and neutron powder diffractometers, analysed by pattern treatment routines (ALLHKL, CSD, MDI-Shadow), and indexed (TREOR, DICVOL91, MDI-Index). The structures were solved using Patterson, Fourier and direct methods (XTAL, SHELXS-86, CSD), and refined using the Rietveld method (DBWS, SIMREF). The structures have between 9 and 152 atoms per unit cell, their symmetries range from cubic (Ca₄Mg₄Fe₃H₂₂) to monoclinic (Mg₂NiH₄), and the atom arrangements have up to 63 free positional parameters (Mg₆Co₂H₁₁). The structure determinations benefited from the high diffraction contrast between the X-ray and neutron data and the possibility of joint refinements of several data sets (SIMREF}, but suffered from the presence of impurity phases in the samples, the bad crystallinity of some hydride phases, and the low resolution of conventional diffraction data.