Abstract: High-pressure hydrogen production via water electrolysis holds great promise because it directly integrates with hydrogen storage and transportation processes, eliminating the need for additional mechanical compressors. Proton exchange membrane (PEM) water electrolysis has been widely adopted for high-pressure hydrogen production, offering advantages in energy consumption and capital cost reduction. This review comprehensively summarizes the recent advancements in high-pressure hydrogen production through PEM water electrolysis, highlighting the progress made in the design of high-pressure PEM electrolysis cells and the integration of high-pressure hydrogen production systems. Compared with traditional methods, which generate hydrogen at ambient pressure and rely on mechanical compression, PEM water electrolysis systems demonstrate higher integration and superior energy efficiency within specific pressure ranges. However, under high hydrogen pressure conditions, hydrogen crossover results in reduced hydrogen production efficiency and increased hydrogen-in-oxygen content, which remain critical challenges. Research into the mechanisms of hydrogen crossover in PEM electrolysis cells has been instrumental in identifying potential mitigation strategies. It has been demonstrated that the hydrogen crossover rate increases linearly with the water electrolysis current density. Two primary models have been proposed to explain this relationship: the pressure-enhancement model and the supersaturation model. Several strategies have been explored to mitigate hydrogen crossover, such as employing the thicker proton exchange membrane, modifying the backbone and functional groups of proton exchange membranes, and loading hydrogen oxidation catalysts on the anode side of the membrane electrode assembly. While these approaches have shown promise in laboratory settings, challenges such as high costs, technical immaturity, and potential impacts on electrolysis efficiency hinder their large-scale deployment. Additionally, the recently developed decoupled water electrolysis (DWE) technology, which uses redox mediators to separate hydrogen and oxygen evolution reactions temporally or spatially, offers a potential solution to hydrogen crossover. Therefore, we further review the principles and technical characteristics of various DWE systems. Based on the type of mediator, DWE systems can be classified into solid-phase mediator and liquid-phase mediator systems. Solid-phase mediators, such as Ni(OH)₂ and MnO₂, are typically derived from battery electrode materials while liquid-phase mediators, such as V³⁺, VO²⁺, and Fe(CN)₆^4?, are commonly derived from flow battery electrolytes. The advantages and limitations of decoupled water electrolysis for high-pressure hydrogen production are analyzed. The DWE systems are based on solid-phase mediators or liquid-phase mediators, and the reaction types involve electrocatalysis, thermal catalysis, and chemical catalysis. The presented DWE systems for high-pressure hydrogen production have significant technical challenges. For instance, DWE systems based on solid-state mediators need to focus on improving the utilization efficiency of the mediator capacity, while systems based on liquid mediators require enhancements in current density and reductions in operating voltage. Although DWE systems offer notable flexibility and safety, there is considerable space for improvement before these systems can be scaled up for widespread application. This review provides valuable insights into the fundamental mechanisms, research progress, and optimization strategies of high-pressure hydrogen production via water electrolysis.