Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity of the brain. Hans Berger (German) recorded the first human EEG in 1924 and confirmed the alpha and beta activities. In 1935, Gibbs et al. described 3 Hz spike and wave patterns during absence seizures, which began the field of clinical electroencephalography in epileptology. In 1958, Jasper advocated 10-20 system of scalp EEG recording. EEG is currently the most important approach to know the status of epilepsy in the clinical field. In recent years, developments of digital EEG recording and computer analysis promoted new EEG interpretations. The wide-band EEG studies have revealed the correlations between the epileptogenecities, high frequency oscillations (>80 Hz), and DC shift (infra slow waves, <0.1 Hz). More advanced EEG analyses, including network analysis, graph theory and so on, came to clarify the latent meaning of the EEG.