The electroencephalogram (EEG) literally (from the Greek) means the measurement of electricity from inside the head and was first recorded from humans by Hans Berger in 1929. The recording is typically done by placing on the scalp a number of electrodes that measure electrical fields generated by neurons in the brain. Electroencephalography plays an important role in neurology and psychology, because it provides an inexpensive, rapidly applied, noninvasive method of monitoring brain activity. Recent technological advances are also increasing interest in commercial applications of this technology. This entry focuses on biological mechanisms, acquisition, common measures, and clinical applications of EEG.