The neurons of the brain have firing. The normal EEG activity is very weak, at the millivolt or even microvoltage level, and the electrophysiological signal is even weaker after attenuation through the skull and scalp. The EEG signal recorded on the scalp needs to be amplified millions of times by an amplifier to be displayed, making it the EEG information needed by the clinician. Because there are many types of seizures and the performance of each type of seizure is different, modern EEGs are equipped with synchronized high-definition video monitoring to monitor the patient for a long period of time. Once the patient has a seizure, an experienced EEG physician can make a correct diagnosis based on the seizure performance captured by the video combined with the concurrent EEG. The EEG is the most basic and essential test for patients with epilepsy. It plays a crucial role in establishing the diagnosis of epilepsy, defining the type of seizure and type of epilepsy syndrome, locating the epileptogenic focus preoperatively and intraoperatively, and assessing the outcome of treatment postoperatively. Depending on the evolution of the disease and clinical needs, many patients may require multiple EEGs.