Electroencephalography(EEG) involves the recording and analysis of electrical signals generated by brain. Resolution of true electrical brain activity requires three elements: good equipment, meticulous recording technique, and informed interpretation of data. Every electroencephalographer should be familiar with the science and engineering underlying clinical EEG. This article reviews principle of EEG instrument & methods of recording; History of EEG, EEG instrument, EEG amplifier & its control, Calibration, Electrode, Electrode placement, Montage, and Electrical safety.