In Britain each year there are approximately 100,000 people who suffer their first ever stroke and only about 14% of the two thirds who survive regain useful upper limb function. While often some ability to make a voluntary grip remains, the ability to selectively activate extensor muscles to enable release of a grasp is frequently lost. Preliminary clinical work confirmed the work of other groups that electrical stimulation exercises of fingers, thumb and wrist lead to an increase in functional ability. An improvement in sensory ability was also shown for the first time. Other studies showed that functional gains are often short lived. It is therefore postulated that if gains are to be achieved and maintained, electrical stimulation must be continued long term. By provision of a functional electrical stimulation (FES) based orthosis, the user may be encouraged to continue using the device because of the immediate benefits received. As use of the device would be associated with functional tasks, there may be greater potential for retraining of movement. Two types of device were developed. The first based on shoulder mounted switches, designed to be immune to misalignment by the user. The second type of device used the electromyogram (EMG) signal from the muscle that was being stimulated to control the stimulation. A novel method of removing the stimulation and M wave artefact was developed enabling the intensity of the stimulation to be controlled by the EMG envelope. Additionally, the stimulation could be triggered by EMG activity or maintained at a fixed level for as long as EMG activity was maintained. The devices were tested in a series of case studies and factors effecting their uses explored. In particular it was noticed that the effort in using a device directly impacted on the use of the device, increasing spastic tone and resisting the opening of the hand. In general, shoulder mounted switches had least effect on tone followed by EMG triggered stimulation, then EMG maintained stimulation and finally EMG proportional stimulation. It was observed that voluntary EMG activity was modulated by the stimulation and this effect was investigated further. From a review of the literature a model of the principle peripheral nervous system motor control structure was developed. The model was expressed in a series of linear equations and the effect of electrical stimulation examined. A series of experiments were devised to examine the effect of electrical stimulation on voluntary EMG. An apparatus for measuring isometric wrist torque while recording extensor and flexor EMG and a data acquisition system was constructed. Measurements with subjects with normal neurology confirmed the effect in the extensors and additionally in the flexor muscle groups. Graded voluntary effort and stimulation intensity tests enabled the main neurological processes to be identified and the majority of effects predicted by the model were observed. Using a widow averaging technique, the effect of the system gain of the interaction of voluntary effort and stimulation intensity was examined. A second series of graded tests investigated the effect of sensory stimulation on EMG activity. Inhibition was seen in both muscle groups and is likely to be due to the involvement of type III afferent fibres. It is likely that the later inhibitory effects seen in motor stimulation are of the same origin.