This paper presents the current state of research into power-assist exoskeletons for the upper limb. The assist of the upper limb is important for physically weak persons in daily activities, since upper-limb motion is involved in many important motions in daily living. The most important criterion is that power-assist exoskeletons assist the user's motion automatically in accordance with the user's motion intentions. Electromyogram (EMG) signals in which the user's motion intention is reflected could provide vital real-time information to facilitate accurate control of the power-assist exoskeleton in accordance with the user's motion intentions. A four degree-of-freedom active exoskeleton that assists human upper-limb motion (shoulder vertical flexion/extension, shoulder horizontal flexion/extension, elbow flexion/extension, and forearm supination/pronation) is also proposed.