The photochemistry of the ferrous ion in the presence and in the absence of oxygen was investigated in the pH region 0.35-3.0. The pH dependence of the initial quantum yield up to pH 2.5 in the presence and absence of oxygen is interpreted as arising from the dependence on H+ ion concentration of the rate of introduction of H atoms into the bulk. This results in the dependence of the quantum yield on √[H+]. A mechanism to account for this is proposed. Another pathway leading to the pH independent formation of H atom also is postulated. The oxidation and reduction processes of the H atoms thus formed are investigated and it is shown that the oxidation of Fe2+ by H atoms may proceed by way of a hydride intermediate. Specific velocity constants are derived. The results of the photochemical experiments are correlated with those obtained in radiation chemistry.