Foot-drop is one of the most common causes of walking disability. To treat the afflicted person, four approaches have been developed which Ankle Foot Orthosis is the most efficient and dominant one. Various designs are developed in the last few years and the trend is towards making these devices more compatible to people lives and providing the required functionality. This paper reviews a variety of designs with their relevant actuating mechanisms, characteristics, advantages and drawbacks. Identifying the critical requirements for an intelligent ankle foot orthosis, a new approach to development of intelligent structures and mechanisms is discussed and analyzed.