Machine Readable Cataloguing 21 (MARC 21)

1. Introduction: MARC 21 is a standard format for the markup or representation and communication of bibliographic data and related information in machine readable form. It is a representation and communication of bibliographic and related information in machine-readable form. It provides a framework for catalogue record. It is widely used to enter the records for the online catalogue so that the bibliographic information can be exchanged among automated library systems by way of copy cataloguing and other means. However, not everything in MARC is captured on OPAC display of a record. MARC 21 is a result of the harmonization of USMARC and Canadian MARC (CANMARC). The MARC 21 standards include formats for authority records, holding records, classification schedules and community information in addition to the format for bibliographic records.

ISO 2709 defines how the marked up record is formatted so that it can be read by computer programs and can be transferred among computers.  ISO 2709 is usually referred to as the MARC communications format.

It was developed by Henriette Avram at the US Library of Congress during the 1960s to create records that can be used by computers, and to share those records among libraries.

The Network Development and MARC Standards Office is a center for library and information network standards and planning in the Library of Congress. Established in 1976 to provide focus for networking activities in the Library of Congress, the office was expanded in 1984 to include MARC standards responsibilities. In 1987, the Library of Congress issued the first edition of the document MARC 21. Subsequent editions were published in 1990, 1994 and 2000.

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.


2. 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.


3. Standard Used in MARC 21: The following standards are used in the MARC-21 format.

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.

4. MARC Tags and Subfields: The data in a MARC 21 record is organized into fields, each identified by a three-character tag. Although ANSI Z39.2 and ISO 2709 allow both alphabetic and numeric characters, MARC 21 formats use only numeric tags.

0XX - Control information, numbers, and codes

1XX - Main entry

2XX - Titles and title paragraph (title, edition, imprint)

3XX - Physical description, etc.

4XX - Series statements

5XX - Notes

6XX - Subject access fields

7XX - Added entries other than subject or series; linking fields

8XX - Series added entries; location, and alternate graphics

9XX - Reserved for local implementation

0XX: The leader (000), control number (001), MARC code for organization (003) and date and time of last transaction (005) are computer generated fixed fields and the cataloguer has no control over it. 001 field is generated by the OCLC, LC or the library management system that is used to create the record. The coded general information (008) is partially computer generated fixed fields.

1XX: The main entry fields are not repeatable.


5. MARC 21 Structure: The structure of MARC record is divided into three elements-Record structure, content designation and data content of the record.

a) Record Structure: The record structure is an implementation of the international standard Format for Information Exchange (ISO 2709) and its American counterpart, Bibliographic Information Interchange (ANSI/NISO Z39.2). It is the overall framework for the record.

b) Content Designation: Content designation is set of symbols by which data in the record are identified and manipulated. The codes and conventions established explicitly to identify and further characterize the data elements within a record and to support the manipulation of that data.

c) Content of the Data:  Content of the data are record specific information field by field. Content of the Data elements is usually defined by standards outside the formats. Examples are the International Standard Bibliographic Description (ISBD), Anglo-American Cataloguing Rules, Library of Congress Subject Headings (LCSH), or other cataloging rules, subject thesauri, and classification schedules (DDC, UDC, etc) used by the organization that creates a record. The content of certain coded data elements is defined in the MARC formats (e.g., the Leader, field 007, field 008).

6. General Record Structure of MARC 21: The general structure of a record is represented schematically below.




a) Leader: Each record begins with a leader, which is fixed field containing information for the processing of the record. The leader is the first field in the record and has a fixed length of 24 octets (character positions 0-23). Only ASCII graphic characters are allowed in the Leader. This is something the cataloguer do not have much control. Only a fee coded data are needed to be determined by the cataloguer i.e. type of record, bibliographic level.

b) Directory: The directory begins immediately after the leader. The directory is generated by the computer for locating data fields with the help of their address. The address mechanism comprises there components-field tag, field length and starting position, which are place consecutively without any space in between. Each directory entry is 12 characters in length. The directory begins in character position 24 of the record. The first three digit of each entry contains tag, following each tag the next four positions show the length of the field and the next five positions tell the starting point for the field. The directory ends with a field terminator (FT), ASCII control character 1E(hex).

c) Variable Fields: The variable fields follow the leader and the directory in the record and consist of control fields and data fields. Control fields precede data fields in the record. The data content has the related bibliographic data as data fields. Two kinds of content designations are used within variable data fields: indicators and subfield codes. The indicators are two one-character positions that contain values that interpret the data found in the field. Every field does not have the indicator. Each subfields code is preceded by a character called delimiter and is followed by an alphabetic or numeric character.


Table 1: MARC Tags with Indicators and Subfields Codes

MARC 21 Tags



Subfield Code

Display Constant / Code / Meaning / What to Input


Main entry

Personal name











Family name



Table 2: Parts of a Catalogue Entry

Personal name             Herath, R. M., author


Table 3: Representation of the Entry in MARC 21 Formats

100      1_        $a Herath, R. M., $e author.


7. Conclusion: Machine-readable cataloguing for assigning labels to various parts of a bibliographic record is a convenient method in which information can be identified and used by computers. The structure of a machine readable record is known as format. MARC 21 is a general format for representing bibliographic information and is a standard for the representation and communication of data in machine-readable form. MARC format has become a generic term to all MARC formats including UKMARC, CANMARC, InterMARC and is used for the identification, arrangement of bibliographical data for handling by computer. The USMARC format became the U. S. National Standard in 1971 (ANSI Z39.2) and an International Standard in 1973 (ISO 2709). To solve the problem of incompatible nature among different countries, IFLA launched a programme known as UNIMARC. UNIMARC followed the ISO communication format ISO-2709 (1981), but it failed. The UNESCO also came up with CCF, which is the implementation of ISO-2709 to solve the problem of incompatibility. Several countries have adopted this standard for exchange and creation of bibliographic record at national level. The MARC 21 is a new name of harmonization of CANMARC and USMARC in a single edition. It uses the standard AACR II, LCSH, DDC, 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.

How to Cite this Article?

APA Citation, 7th Ed.:  Barman, B. (2020). A comprehensive book on Library and Information Science. New Publications.

Chicago 16th Ed.:  Barman, Badan. A Comprehensive Book on Library and Information Science. Guwahati: New Publications, 2020.

MLA Citation 8th Ed:  Barman, Badan. A Comprehensive Book on Library and Information Science. New Publications, 2020.