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. These compounds are interesting materials for hydrogen storage applications. During the past few years some 20 ternary alkaline earth hydrides and complex ternary and quaternary transition metal hydrides were characterized. Diffraction data were collected on deuterides by using X-ray (Guinier), synchrotron and neutron powder diffractometers, analyzed by pattern treatment routines (ALLHKL, MDI-Shadow), and indexed (MDI-Index, TREOR). The structures were solved by using Patterson, Fourier and direct methods (XTAL, SHELX, CSD), and refined by using the Rietveld technique (DBWS, SIMREF). The structural 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 X-rays and neutrons and the possibility of joint refinements of several data sets (SIMREF), but suffered from the presence of impurity phases in the samples and the bad crystallinity of some hydride phases. The results obtained were essential for establishing the correct chemical formula, and for a better understanding of parameters of technological importance, such as maximal hydrogen content and thermal stability.