Robotic exoskeleton is getting important to human in many aspects such as power assist, muscle training, regain motor function and rehabilitation. The research and development towards these functions are expected to be combined and integrated with the human intelligent and machine power, eventually becoming another generation of robot which will enhance the machine intelligent and human power. This paper reviews the upper extremity exoskeleton with different functions, actuators and degree of freedom (DOF). Among the functions, rehabilitation and power assist have been highlighted while pneumatic actuator, pneumatic muscle, motor and hydraulic actuator are presented under the categories of actuator. In addition, the structure of exoskeleton is separated by its DOF in terms of shoulder, elbow, wrist and hand.