We are requesting funding for an essential need in neuroscience, supporting researchers with chronically-implantable multisite microelectrode arrays. Microelectrode arrays are an important tool for neural prostheses and brain machine interfaces as well as for basic neuroscience. Clinical applications now under development include central auditory prostheses that utilize electrical neural stimulation to overcome hearing loss, visual prostheses employing microstimulation in the cerebral cortex, and closed-loop deep brain stimulation to relieve the motor symptoms of Parkinson's disease and other disorders. While there are commercial vendors providing microwire arrays and silicon arrays suitable for chronic implantation, there is an unmet need for custom-assembled silicon-based 3D multisite microelectrode arrays. This resource center will design, fabricate, and assemble customized microelectrode arrays for long-term neural stimulation and recording in-vivo. The proposed devices will be fabricated from custom-designed multisite silicon-based arrays that can be inserted into targets in the sulci of the cerebral cortex, deep brain, brainstems, and spinal cord or spinal nerves. The devices will be mechanically sturdy for reliable insertion into the target tissues, and will have long flexible cables to meet users' requirements. The arrays are intended to be used in animal models such as rats, cats, and non-human primates, and are designed to facilitate clinical translation.