Three dislocation models are investigated for explaining the hydrogen embrittlement of refractory (b.c.c.) metal alloy single crystals and large-grain polycrystals on the basis of cleavage initiation. The models considered are: (1) stress-induced dislocation pile-ups and dislocation reactions; (2) hydrogen-enhanced decohesion of slip plane pile-ups and planar dislocation arrays; and (3) slip and hydrogen interactions with lineage subgrain boundaries. Emphasis is given in each case to the crystallographic features of low strain cleavage initiations in the presence of hydrogen as observed in three refractory alloy systems. Electron microscope observations, including the occurrence of deformation twinning, are presented for the hydrogen-charged materials as a function of strain. Cumulative (low energy) stress fields are described for the dislocation pile-ups and the lineage boundaries. The enhancement of hydrogen concentration in the presence of the stress fields of these dislocation configurations is determined. The slip-twinning relationship and cleavage associated with hydride microprecipitates are considered.