Hydrogen-enhanced localized plasticity (HELP) is a mechanism for hydrogen-related fracture. The paper reviews several mechanisms of hydrogen embrittlement, including stress-induced hydride formation, hydrogen-enhanced localized plasticity, and hydrogen-induced decohesion. It focuses on the HELP mechanism, which involves hydrogen reducing dislocation motion barriers, leading to localized plastic deformation near the fracture surface. This process is counter-intuitive as it limits macroscopic ductility by promoting localized plasticity rather than embrittlement. The paper discusses how hydrogen shields dislocations from elastic stress centres, increasing dislocation mobility. It also examines the effects of hydrogen on macroscopic deformation, showing that hydrogen can either increase or decrease flow stress depending on the extent of slip localization and dislocation mobility. The paper presents a theory of hydrogen shielding of dislocation interactions, showing that it can account for the observed hydrogen-enhanced dislocation mobility. It also discusses the effects of hydrogen on slip localization, which can lead to increases or decreases in flow stress. The paper concludes that hydrogen effects on fracture are complex and depend on factors such as hydrogen concentration, strain rate, and temperature. The results suggest that hydrogen shielding of dislocation interactions is a key factor in hydrogen-related fracture. The paper also discusses the effects of hydrogen on the interaction of dislocations with solutes and precipitates, showing that hydrogen can significantly reduce interaction energy. The paper concludes that the mechanisms of hydrogen-related fracture are complex and that further research is needed to fully understand the role of hydrogen in fracture.Hydrogen-enhanced localized plasticity (HELP) is a mechanism for hydrogen-related fracture. The paper reviews several mechanisms of hydrogen embrittlement, including stress-induced hydride formation, hydrogen-enhanced localized plasticity, and hydrogen-induced decohesion. It focuses on the HELP mechanism, which involves hydrogen reducing dislocation motion barriers, leading to localized plastic deformation near the fracture surface. This process is counter-intuitive as it limits macroscopic ductility by promoting localized plasticity rather than embrittlement. The paper discusses how hydrogen shields dislocations from elastic stress centres, increasing dislocation mobility. It also examines the effects of hydrogen on macroscopic deformation, showing that hydrogen can either increase or decrease flow stress depending on the extent of slip localization and dislocation mobility. The paper presents a theory of hydrogen shielding of dislocation interactions, showing that it can account for the observed hydrogen-enhanced dislocation mobility. It also discusses the effects of hydrogen on slip localization, which can lead to increases or decreases in flow stress. The paper concludes that hydrogen effects on fracture are complex and depend on factors such as hydrogen concentration, strain rate, and temperature. The results suggest that hydrogen shielding of dislocation interactions is a key factor in hydrogen-related fracture. The paper also discusses the effects of hydrogen on the interaction of dislocations with solutes and precipitates, showing that hydrogen can significantly reduce interaction energy. The paper concludes that the mechanisms of hydrogen-related fracture are complex and that further research is needed to fully understand the role of hydrogen in fracture.