Recent advances in the understanding of solid-solution hardening (SSH) of crystalline materials, as well as some basic early papers are briefly reviewed. This survey shows that models of SSH based on the concept of a frictional drag on dislocations migrating through fields of point-like obstacles, whether randomly dispersed or clustered, do not encompass the principal features of SSH, e.g. the temperature dependence of the yield stress, the stress and temperature dependences of the activation volume, and the phenomenon of stress equivalence. However, a model based on the nucleation of slip, involving the breakaway of dislocation segments from several pinning points, formulated in closed form, is shown to account satisfactorily for the principal observations.