Present motor-system neural prostheses use electrical activation of last-order (motor) neurons to restore function. We are pursuing a new approach: restoration of function by electrical activation of higher-order interneurons. Our hypothesis is that electrical activation of spinal neural circuits, rather than direct activation of last-order motoneurons, will simplify generation of complex motor behaviors. We review two approaches to control bladder function and to control skeletal motor function: intraspinal microstimulation for direct activation of spinal neurons and peripheral afferent stimulation for indirect, synaptic activation of spinal neurons. The results demonstrate that electrical activation of spinal neural circuits allows generation of complex motor behaviors including micturition and organized multi-joint motor responses with a single electrode. Electrical activation of spinal neural circuits, and generation of the complex functions they subserve, holds great promise to advance the function of motor system neural prostheses.