The purpose of this study is to investigate historical backgrounds, maintenance, revision and application areas of UDC(Universal Decimal Classification) in order to understand current issues of it systematically. Since 1905, n has been extensively developed and is now administered by UDC Consortium(UDCC). UDCC updates MRF(Master Reference File), an electronic form of the UDC schedules, once a year. UDC updates and publishes standard edition extended edition, and abridged edition according to the degrees of notion abridgement, and is available on the web. UDC can be now applicable to collection arrangement, SDI(Selective Dissemination of Information) service, searching subject bibliographies, switching language or subject gateway and metadata on the Internet, and automatic classification.