Abstract: As a key aspect of transition prediction and control, receptivity process in hypersonic boundary layer is of great importance. However, it still has not been thoroughly understood, and is especially lacking in experimental verification. In this paper, two categories of disturbances are reviewed, namely, free-stream disturbance (acoustic, vertical, thermal perturbation, shock wave and particulates) and wall-induced disturbances (roughness, vibration, blowing and suction, surface heating and cooling). Mostly concerned are the theory of Fedorov about leading-edge receptivity and inter-modal exchange mechanism. In order to make the issue of receptivity more clearly understood, a compendious path diagram is sketched to describe paths to Mack modes.