The coupling of compositional and crystal-structural effects creates particular conditions for hydrogen embrittlement (HE) in high-alloyed austenitic steels. Austenitic stainless steels are commonly more compatible with hydrogen-bearing environments than ferritic alloys, and the austenitic stainless steels are often specified for hydrogen service when their enhanced compatibility, safety, and reliability override their expense. The tensile yield strength of an austenitic stainless steel typically increases only slightly or may decrease slightly when specimens are precharged with hydrogen. It is clear that microstructure is “the more fundamental” contributor to properties in hydrogen and must be considered in the steels. The hydrogen-induced phases are sometimes considered as pseudo-hydrides. It is generally assumed that the role of hydrogen amounts to the creation of a particular stress state that triggers the phase transformation. The quantity of hydrogen that dissolves into a stainless steel for a given temperature and hydrogen fugacity, how that hydrogen is distributed, and the hydrogen mobility have an important bearing upon how hydrogen affects the physical and mechanical properties of the steels. For many stainless steels, significant acceleration of fatigue growth rate is seen after hydrogen charging. A decrease in the appearance of slip planes could be associated with the increased localization of plasticity at the surface of hydrogen-charged stainless steel. Hydrogen-enhanced localized plasticity (HELP) is responsible for the degradation of the reduction of area (RA) in stainless steels thermally precharged with gaseous hydrogen.