<p>This review provides recent advancements in the study of attachment-line boundary layer transition with emphasis on high-speed configurations. As a critical factor influencing aerodynamic performance and thermal management in supersonic and hypersonic systems, the transition mechanisms of three-dimensional attachment-line boundary layers have emerged as a pivotal research frontier in high-speed aerodynamics. This review systematically summarizes the evolution of research on attachment-line boundary layer transition, from early theoretical foundations to modern computational and experimental breakthroughs. A critical examination is presented for two pivotal challenges in high-speed attachment-line boundary layer transition: The resolution of the Gaillard paradox and the leading-edge contamination mechanism. Through systematic synthesis of theoretical developments and empirical evidence, this review identifies critical knowledge gaps while proposing novel methodological approaches for attachment-line boundary layer transition analysis. The review culminates in a strategic framework outlining promising avenues for both fundamental inquiry into attachment-line phenomena and applied engineering solutions in flow control strategies.</p>