The overall objective of this project was to leverage our labs expertise in cortical neuroprosthetics with emerging viral optogenetic techniques in peripheral nerves to produce a hybrid, brain-controlled Functional Optical Stimulation (FOS) system in non-human primates, which would offer several advantages over traditional Function Electrical Stimulation (FES) systems to restore volitional motor control. Initial experiments were used to evaluate the efficacy of several viral vectors, including adeno-associated virus (AAV) and non-replicating rabies virus (NRRV) constructs, in transducing light- sensitive opsins into peripheral motor nerve axons in macaques and rats. The results of these experiments showed successful yet highly variable expression with several AAV constructs, but no detectable expression of optogenetic products when using NRRV-based constructs. Evaluation of several injection techniques suggested that spinal cord injections of virus were the most consistent in eliciting gene expression but the least specific in targeting specific muscles, while muscle injections showed variable expression but demonstrate muscle specific labeling of motor nerve fibers. Next, a new opsin, Chronos, demonstrated desirable light sensitivity and channel kinetics over the traditionally used opsin, ChR2. Finally, a prototype micro-LED nerve cuff was designed and tested for chronic stimulation of opsins tranduced in peripheral nerves.