Recent developments in neurophysiological methods have broadened our understanding of the human brain and improved management of neurological disorders. Electric source imaging (ESI) is a non-invasive technique which applies mathematical algorithms to localize the source of a given electroencephalogram (EEG) or evoked potential (EP) pattern in real time. This technique allows reconstructing brain activity measured from scalp electrodes and can be applied in the individual patient to fit different clinical purposes. ESI based on high-density EEG recordings significantly improved non-invasive preoperative evaluation of epilepsy surgery and helped to include patients previously not considered surgical candidates. In experimental settings, ESI is performed to localize areas involved in sensory processing. Brain source imaging of somatosensory evoked potentials (SEP) are employed during presurgical planning to localize the functional cortex and to avoid this region during lesion resection. Research laboratories apply ESI to chemosensory event-related potentials (CSERP) to elucidate the spatial and temporal dynamics of the olfactory pathway. Nowadays, ESI is used for either clinical or research purposes, since it provides objective measurements of brain mapping that cannot be achieved by conventional analysis which are restricted to the scalp surface.