Graphene‐like single‐ or few‐layer semiconductors, such as dichalcogenides and buckled nanocrystals, possess direct and tunable bandgaps, and excellent electrical, optical, mechanical and thermal properties. This unique set of desirable properties of 2D semiconductors has triggered great interest in developing ultra‐thin 2D flexible electronic devices, which ranges from realizing better material quality and simplified fabrication processes, to improving device performance and expanding the application horizon. The most explored 2D flexible devices based on transition metal dichalcogenides and black phosphorous include field‐effect transistors, optoelectronics, electronic sensors and supercapacitors. By taking advantage of a large portfolio of materials and properties of 2D crystals, a new generation of low‐cost, high‐performance, transparent, flexible and wearable devices looks attractive and promising in advancing flexible electronic technologies. 2D semiconductors have become an emerging and important choice of materials for flexible high‐performance electronics, due to their merits of extraordinary, tunable electrical and mechanical properties. Recent advancements in material growth, mechanical design, and device fabrication are reviewed, along with detailed examples of flexible device applications. Possible routes to obtain stretchable devices and the challenges of realizing multifunctional system‐scale flexible devices are also discussed.