Definition and scope:

The variable data fields include fields 01X-8XX.  They are grouped into blocks according to the first character of the tag, which, with some exceptions, identifies the function of the data within the record.  The type of information in the field is identified by the remainder of the tag.  Each field is identified by a field tag in the Directory.  Within variable data fields, two kinds of content designation are used:  two indicator positions which are at the beginning of each field; and, a two-character subfield code which precedes each data element within the field.

The following are General Information sections for groups of fields with similar characteristics.:

Classification Numbers:  Indicators, subfield codes, and input conventions for the classification number fields follow similar patterns.  For detailed information, select:  X53 Classification Numbers.

Tracings and References:  Describes tracing fields, reference note fields, simple and complex cross references including examples, input conventions, etc.  For detailed information, select:  Tracings and References - General Information.

For information on a specific variable data field, select a topic:

(Shortcut:  For information on a particular field, use the Tag Lists to search by tag, subject area, or alphabetically.)

Tag range:

Field description:


Numbers and Codes


Classification Numbers and Terms


Tracings and References




Index Terms


Number Building Fields


Other Variable Fields

See also:

Variable Control Fields

MARC 21 Format for Classification Data:  Contents