Machine Readable Cataloguing 21 (MARC 21): The MARC 21 is a standard format for the representation and communication of bibliographic and related information in machine readable form. The MARC 21 is a new name of harmonization of CANMARC and USMARC in a single edition. In 1987, the Library of Congress issued the first edition of the document MARC 21. Subsequent editions were published in 1990, 1994 and 2000.
a) Necessity of MARC 21: Mark 21 is necessary because of the following factors:
i) Lack of standardization among different national MARC formats;
ii) Lack of internationally accepted cataloguing code to MARC record;
iii) Diverse functions of bibliographic agencies;
iv) Lack of agreement among different bibliographic communities.
b) Maintenance of MARC 21: The Library of Congress and the National Library of Canada serve as the maintenance agency for MARC 21. The MARC 21 format, documentation and reviewing and revision are done by the Machine Readable Bibliographic Information Committee (MARBI). MARBI is a committee of the ALA. MARBI meets in conjunction with MARC advisory committee at each American Library Association (ALA) conference.
c) Standard Used in MARC 21
i) Cataloguing Code: AACR II;
ii) Subject Heading: LCSH;
iii) Classification Scheme: DDC;
iv) ISO 2709 and ANSI / NISO Z39.2.
Till now, MARC 21 remains the standard one which is widely accepted in different library softwares and also in different countries.