A concept for hydrogen-caused embrittlement of austenitic steels is proposed based on the ab initio calculations and experimental studies of the electron structure. It is obtained that hydrogen increases the density of electron states at the Fermi level and, correspondingly, the concentration of free electrons. As a result, the metallic character of interatomic bonds is enhanced within the clouds of hydrogen atoms around the dislocations, which locally decreases the shear modulus and produces the softening effect. Based on the effect of alloying elements on the electron structure of austenitic steels, their influence on hydrogen brittleness is predicted and tested. The hydrogen-caused localization of plastic deformation is interpreted in terms of hydrogen-increased concentration of thermodynamically equilibrium concentration of vacancies.