<p>Hydrogen embrittlement (HE) remains a critical challenge in materials engineering, particularly for metals and alloys used in hydrogen fuel cell technologies. This review identifies the underlying problem of mechanical degradation caused by hydrogen–metal interactions, which compromise the ductility, toughness, and structural reliability of these materials. The study focuses on reviewing the main mechanisms of HE—namely Hydrogen Enhanced Local Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE), and the Hydrogen Pressure Theory—and their relevance to energy applications. A systematic review approach was adopted, integrating findings from experimental, theoretical, and computational studies to analyze how microstructural features and environmental factors influence susceptibility to HE. The review covers key experimental techniques such as Thermal Desorption Analysis (TDA), Atom Probe Tomography (APT), and in situ Scanning Electron Microscopy (SEM), which have advanced the understanding of hydrogen behavior in metals. Findings indicate that microstructural control and alloy design significantly affect hydrogen trapping and fracture behavior. Based on these discoveries, the study recommends the development of hydrogen-tolerant materials through microstructure optimization and advanced surface engineering. In conclusion, the review provides a comprehensive framework for mitigating HE in emerging hydrogen energy systems, promoting safer and more durable materials for sustainable energy applications. These findings not only identify key research priorities for advancing fundamental understanding of hydrogen–metal interactions but also offer practical guidance for designing hydrogen-tolerant alloys and improving the reliability of materials used in fuel-cell and hydrogen-energy systems.</p>