MARC21

MARC 21 is a standard for the representation and communication of bibliographic and related information in machine-readable form. It is part of the MARC family of standards used by libraries to describe items in catalogs and to support resource discovery, interlibrary loan, and data exchange. MARC 21 was developed by the Library of Congress in collaboration with national libraries and international bibliographic communities to provide a single, globally usable framework for bibliographic data. The standard defines three primary formats: MARC Bibliographic, MARC Authority, and MARC Holdings, each tailored to different kinds of library records.

Records in these formats share a common structure: a leader, a directory, and a sequence of data or control fields. Each field is identified by a three-digit tag, contains indicators, and carries subfields identified by single-character codes. Data fields hold core bibliographic information such as titles, authors, publication data, and subjects; authority fields provide controlled access points for persons, corporate bodies, and topics; holdings fields describe item location and availability.

MARC 21 supports two character encodings: MARC-8 and Unicode UTF-8, enabling representation of many scripts. It accommodates modern cataloging practices, including Resource Description and Access (RDA), through specific data elements such as 336 (Content Type), 337 (Media Type), and 338 (Carrier Type). Records can be exchanged in various representations, including MARC-XML and MARCJSON, supporting integration with contemporary metadata workflows.