Electroencephalography (EEG) records brain electrical activity at the scalp level. As a functional and non invasive witness of brain activity, EEG has long raised the interest of researchers and practitioners, notably in the domain of anesthesia. Thanks to technical advances, this complex signal can now be dissected, and a huge amount of information can be extracted from it. This information gives the opportunity to quantify theeffects of general anesthesia on the brain, and provides a better understanding of the underlying mechanisms.