Abstract: This paper focuses on the hydrogen embrittlement (HE) susceptibility of pipeline steel welded joints. A systematic elaboration is provided on the material characteristics (microstructural constituents and phase interface features), hydrogen sources (internal hydrogen from manufacturing/processing residues and external hydrogen from environmental permeation), and the HE mechanism (synergistic effect of hydrogen diffusion, enrichment, and crack propagation). Primary emphasis is placed on the analysis of the dominant factors governing HE susceptibility, which include material characteristics, mechanical conditions, and environmental factors.