The effects of solutes on dislocation behavior have been extensively studied over many years. Among this body of literature is a very large amount of work on the effects of hydrogen on dislocation behavior and on plastic deformation. These studies are closely related to the very much larger body of work on hydrogen effects on fracture. In this paper, we focus on the influence of solute hydrogen on dislocation behavior, the manifestation of these effects on the plastic deformation of solids and, finally, present some mechanistic approaches that allow the rationalization of the very diverse set of observations. We do not discuss the effects of hydrogen on the fracture of solids.