Abstract: Pipelines, especially the existing natural gas pipelines, are integral to the entire value chain of the full-scale hydrogen economy, contributing to accelerated energy transition. However, hydrogen embrittlement potentially occurring on pipelines threatens the pipeline operating safety and constrains the development of hydrogen pipeline industry. In this work, the scientific meaning of hydrogen embrittlement was explained, along with the conditions, steps and mechanisms for hydrogen embrittlement occurrence, while many confusions and misunderstandings were clarified and corrected. Particularly, the differences between hydrogen embrittlement in “aqueous”environments and the hydrogen embrittlement in “gaseous” environments were distinguished. Besides, the unique characteristics and the technical challenges of hydrogen embrittlement of pipelines were summarized. Based on the latest research achievements and personal academic communication experience in high-pressure gaseous hydrogen embrittlement, the gaps existing in both scientific and technical aspects for hydrogen embrittlement of pipelines were identified, so as to provide technical support to the safe operation of pipeline for hydrogen transport in blending form. (4 Figures, 2 Tables, 24 References)