AbstractHydrogen embrittlement (HE) is considered to be part of stress corrosion cracking (SCC) problem and as a phenomenon of its own. In the first part of the review the present day methods for an identification of the role of HE in SCC are discussed and a general approach for any construction material is proposed to solve this question. The second part is concerned with those aspects of the HE theory which; are still not clear (acoustic data, the disposition of the fracture zones by HE ahead of the crack tip, critical hydrogen concentration) and with some newly proposed experiments.