An important goal in neuroscience is to understand how the assembly of neuronal circuits contributes to the emergence of function controlling dedicated animal behaviors. Motor behavior represents the ultimate output of nearly all nervous system activity. An intricate network of neuronal circuits within the spinal cord communicating bi-directionally with higher centers in the brainstem and brain, as well as integrating sensory feedback from the periphery ensures the accuracy of motor output. Despite its seeming complexity, the final motor output system displays an exquisite degree of organization, and is experimentally accessible at a high degree of specificity, using genetic, molecular, anatomical and physiological analysis linked to a direct behavioral output. The overall goal of our studies will be to extract information on how – at the neuronal circuit level – specificity of connections in the motor system can explain behaviors as complex as motor behavior. Our major focus over the next several years will be to contribute to our understanding of how motor circuits influence and regulate the activity of functionally defined groups of motor neurons in the spinal cord.