Abstract:Progress in bypass transition induced by free-stream disturbance is reviewed in this paper. Free-stream disturbance, as the forcing environment, can be divided into two categories, free-stream turbulence and wake. The definition, classification and general route of bypass transition is presented first, followed by reviewing the characteristics and physics of FST-induced bypass transition. In this scenario, the topics of receptivity process, transient growth theory, Klebanoff mode, streak instability, turbulent spot and breakdown have all been covered. Moreover, we go further to review the previous studies on bypass transition induced by wake, both the passage wake and the wake containing large scale coherent vortices are included. Finally, the perspective for future investigations is forcasted.