It is sought to relate the diffusion coefficient and solubility for hydrogen in metals to the interaction of hydrogen with the metal phase. Determinations of permeation and diffusion coefficient have been made by a very sensitive electrochemical method at room temperature, and in some cases with temperatures up to 80°C, for platinum, nickel, tantalum, titanium, zirconium, manganese, and iron-chromium alloys.The dependence of permeation at high cds on time varies qualitatively with the metal involved. The diffusion coefficient for iron-chromium alloys decreases with increasing chromium; the solubility increases with increasing chromium. In general, the solubility decreases with increasing heat of absorption, and decreases with decreasing d-vacancies. The diffusion coefficient decreases with increasing latent heat of sublimation of the metal.The critical concentration of hydrogen that causes embrittlement in the metal is interpreted in terms of a model involving the pressure of hydrogen in voids. Qualitative support is cited. Gas-phase heats of solution of hydrogen in metals are those obtained for the solution case. Solubility of hydrogen depends upon d-vacancies according to a simple model. A solution of equations relating to the diffusion of hydrogen out of pre-charged metal foils is given.