Machine-Readable Cataloging. An international standard digital format for the description of bibliographic items developed by the Library of Congress during the 1960s to facilitate the creation and dissemination of computerized cataloging from library to library within the same country and between countries. By 1971, the MARC format had become the national standard for dissemination of bibliographic data and by 1973, an international standard.
There are several versions of MARC in use in the world, the most predominant being MARC 21, created in 1999 as a result of the harmonization of U.S. and Canadian MARC formats; UKMARC, used primarily in the United Kingdom; and UNIMARC, widely used in Europe. The MARC 21 family of standards now includes formats for authority records, holdings records, classification schedules, and community information, in addition to formats for the bibliographic record.