In 1924, Hans Berger, a German psychiatrist, recorded the brain waves from a human brain for the first time. Many advances have been made in this field since then. Currently, brain waves are generated by a variety of computer technologies, including brain computer interface technology, and robot or artificial intelligence technology has also made amazing progress. A mental health practitioner who deals with brain-related medicine has an obligation and responsibility to research and find clinical applications of brain waves because they contain a great deal of information hidden in the brain. Therefore, understanding the basics of electroencephalography will contribute to a determination and resolution of various clinical situations. This review discusses basic knowledge before dealing with brain waves. In addition to a visual inspection of general brain waves, quantitative analysis of brain waves is expected to become an important area of interest for mental health practitioners.