Previous experimental and theoretical studies of hydrogen charging in Zr alloys are critically reviewed. A previously developed model of the hysteresis in the terminal solid solubility (TSS) of hydride-forming metals is extended to derive an expression for the solubility limit during cooldown in the presence of hydrides and applied to rationalize the extant results on hydrogen charging. The various TSS values and the hysteresis between them is governed by the elastic and plastic components of the elastic-plastic hydride/matrix accommodation energy. These energies vary significantly with temperature as a result of their dependence on the yield stress. In thin samples coated with a hydride layer, the ability of the interior of the sample (under thermal cycling) to increase its hydrogen content above that expected from a simple equilibration with the external layer is explained in terms of this model for TSS hysteresis and the difference in TSS levels between interior and exterior hydrides. The same model can be used to explain the high interior hydrogen levels attainable under isothermal or temperature-cycling hydrogen-ingress conditions. Previous models of hydrogen ingress can account for the observed results if modified to include the TSS hysteresis effects. The model of TSS hysteresis is used to provide an explanation for the effect of direction of approach to test temperature on delayed hydride crack velocity.