Magnetoencephalography (MEG) has advanced dramatically in the past 50 years, since the first neuromagnetic recording in 1968. Recent MEGs have both high spatial resolution of a few millimeters and high temporal resolution in the order of millisecond. MEG is applied not only clinically, but also in many academic fields including physiology and psychology. In this article, the basic principle and structure of MEG, and the brief history of development are described.