Although the mechanism of action of sacral neuromodulation (SNM) is still not fully elucidated, it seems to involve modulation of spinal cord reflexes and brain networks by peripheral afferents according to findings from neurophysiology, electroencephalography, positron emission tomography, and magnetic resonance imaging studies. Moreover, motor effects mediated via efferents on direct stimulation cannot be fully excluded. In this mini-review, we summarize current knowledge on the mechanism of action of SNM. PATIENT SUMMARY: We reviewed the literature on the mechanism of action of sacral neuromodulation, in which electrical stimulation is applied to the nerves that regulate bladder activity. The mechanism seems to involve modulation of spinal cord reflexes and brain networks by peripheral sensory and possibly motor neurons.