Drug resistant epilepsy (DRE) is not an uncommon clinical condition. DRE could cause disabling seizures and even sudden unexpected death in epilepsy (SUDEP). Pre-surgical evaluation is necessary to for surgical treatment to cure or palliative epilepsy. If feasible, surgical excision of an epileptic focus provides the best chance of cure. However, the standard non-invasive workup could not always identify the epileptic focus. Stereotactic EEG (SEEG) is an invasive EEG that could provide the spatial and temporal progression of epileptic discharge so that we could localize or lateralise the epileptic focus more easily. This chapter aims to illustrate the principle of SEEG, the methods of SEEG electrode insertion, the usual white matter tract pathway that epileptic discharge progresses. It also discusses the therapeutic use of SEEG in lesioning with radiofrequency ablation (RFA), as well as the future potential as part of the brain-computer interface (BCI).