Recent advancement of neurophysiologic and radiologic examinations has enabled us to better define epileptic focus or network. Volumetric evaluation with 3 tesla MRI has made it possible to visualize epileptogenic lesions including very minute changes such as tiny focal cortical dysplasia. Stereo–EEG (SEEG) has prevailed in the United States and Europe in the last decade, thanks to the advancement of MRI, brain navigation system and stereotactic electrode placement techniques. SEEG is superior to evaluation with subdural electrode implantation in 1) its ability to sample EEG from the depth of the brain so that we can visualize and define the epileptic focus and early propagation network in three dimensional way, and 2) less invasiveness (no needs to perform craniotomy). Cortico–cortical evoked potential (CCEP) is a novel connectivity method we have developed to electrically trace the brain connectivity by applying a single–pulse electrical stimulation to a part of the cortices and record brain evoked potentials time–locked to the stimulus. Because of its practicality, good reproducibility and safety with regards to seizure induction, CCEP has been used all over the world to 1) probe the epileptic networks and 2) map and monitor the brain functional networks such as language for brain surgeries.