This chapter focuses on the role of neuronal mechanisms underlying gait disorders and the therapeutic consequences. Locomotion is a subconciously performed everyday movement with a high reproducibility. Leg muscle activation during locomotion is produced by spinal neuronal circuits within the spinal cord, the spinal pattern generator. Pathophysiologically, an impaired neuronal control of gait associated with rigid and poorly modulated motor performance represents a major deficit of Parkinson's disease. In patients with Parkinson's disease several studies on gait indicate an impaired programming. Spasticity produces numerous physical signs such as exaggerated reflexes, clonus, and muscle hypertonia. A considerable degree of locomotor recovery in mammals with a spinal cord injury (SCI) can be attributed to a reorganization of spared neural pathways. For future application in the rehabilitation field, gait analysis may help to select the most effective pharmacological and physiotherapeutical approaches.