This review provides an overview of recent advancements in vapor-fed photoelectrochemical (PEC) systems designed to utilize water vapor as a hydrogen resource. The PEC system under water vapor feeding uses a proton exchange membrane (PEM) as a solid polymer electrolyte and gas-diffusion photoelectrodes composed of fibrous conductive substrates with macroporous structures. The porous photoelectrodes are made of n-type oxides for oxygen evolution reactions and used with a Pt electrocatalyst cathode for hydrogen evolution reactions. Key topics include the conceptual framework of vapor-fed PEC hydrogen production, strategic design of gas-phase PEC reaction interfaces, and development of porous photoanodes such as titanium dioxide (TiO₂), strontium titanate (SrTiO₃), tungsten trioxide (WO₃), and bismuth vanadate (BiVO₄). The application of a thin proton-conducting ionomer film on these porous photoelectrodes enhances PEC efficiency through surface functionalization. The rational design of proton exchange membrane-based PEC cells is crucial for realizing renewable-energy-driven hydrogen production from atmospheric humidity. The review also discusses the advantages of using water vapor over liquid water, including reduced maintenance costs, avoided liquid-pumping systems, and minimized freezing risks. The historical overview of PEM-PEC devices and the recent progress in vapor-fed PEC systems are presented, highlighting the importance of the triple-phase boundary concept under gas-phase conditions. The review concludes with suggestions for future work to improve the solar-to-hydrogen (STH) energy conversion efficiency of PEM-PEC cells.This review provides an overview of recent advancements in vapor-fed photoelectrochemical (PEC) systems designed to utilize water vapor as a hydrogen resource. The PEC system under water vapor feeding uses a proton exchange membrane (PEM) as a solid polymer electrolyte and gas-diffusion photoelectrodes composed of fibrous conductive substrates with macroporous structures. The porous photoelectrodes are made of n-type oxides for oxygen evolution reactions and used with a Pt electrocatalyst cathode for hydrogen evolution reactions. Key topics include the conceptual framework of vapor-fed PEC hydrogen production, strategic design of gas-phase PEC reaction interfaces, and development of porous photoanodes such as titanium dioxide (TiO₂), strontium titanate (SrTiO₃), tungsten trioxide (WO₃), and bismuth vanadate (BiVO₄). The application of a thin proton-conducting ionomer film on these porous photoelectrodes enhances PEC efficiency through surface functionalization. The rational design of proton exchange membrane-based PEC cells is crucial for realizing renewable-energy-driven hydrogen production from atmospheric humidity. The review also discusses the advantages of using water vapor over liquid water, including reduced maintenance costs, avoided liquid-pumping systems, and minimized freezing risks. The historical overview of PEM-PEC devices and the recent progress in vapor-fed PEC systems are presented, highlighting the importance of the triple-phase boundary concept under gas-phase conditions. The review concludes with suggestions for future work to improve the solar-to-hydrogen (STH) energy conversion efficiency of PEM-PEC cells.