LC Control Number Structure

The LC control numbering system used with authority records has the same basic structure as that used in control numbers for Library of Congress bibliographic records (LCCN structure A). On January 1, 2001, a structural change occurred (LCCN structure B). The basic control number has been fixed in length at 12 characters and remains that length. Under LCCN structure B, the location of element parts is slightly altered to accommodate a four digit year.

Note: Under both structures, the alphabetic prefix, year, and serial number are the basic elements required to make an LCCN unique.

LCCN Structure A (1978-2000)
Name of element	Number of characters	Character position in field
Alphabetic prefix	3	00 - 02
Year	2	03 - 04
Serial number	6	05 - 10
Supplement number	1	11

LCCN Structure B (2001- )
Name of element	Number of characters	Character position in field
Alphabetic prefix	2	00 - 01
Year	4	02 - 05
Serial number	6	06 - 11

Alphabetic prefix: (3 digits before January 1, 2001; 2 digits after)

Prefixes are carried in a MARC record as lowercase alphabetic characters and serve to differentiate between different series of LC control numbers. Prefixes are left justified and each unused position contains a blank (#). If no prefix is present, the prefix portion contains blanks.

See: Examples

LC authority records are differentiated from other LC records by the control number prefix.

MARC prefix:	Explanation:
n	Name or subject authority record keyed by LC
nb	Name or subject authority record originating in the British Library
nr	Name or subject authority record originating in the Research Libraries Information Network (RLIN)
no	Name or subject authority record originating in the Online Computer Library Center (OCLC)
sh	LCSH subject authority record distributed by LC
sj	Juvenile subject authority keyed by LC and distributed in the LC Annotated Children's Cataloging Program
sp	Subject authority proposal record in the LC catalog. (When it is approved, the record will be distributed with the prefix sh.)

Year: (2 digits before January 1, 2001; 4 digits after)

For control numbers assigned under LCCN structure A, the year portion consists of two digits representing the year the control number was assigned. In name authority records that were converted retrospectively by an agency under contract to LC, the digits 50 were used for the year for name authority records, and the digits 42 were used for series authority records. In subject authority records that were converted retrospectively from an LC internal format to MARC, the digits 85 were used instead of the actual year of creation. For control numbers assigned under the LCCN structure B beginning with the year 2001, the year portion consists of four digits.

Serial number: (6 digits before January 1, 2001; 6 digits after)

The serial number portion consists of one to six digits. Serial numbers of less than six digits are right justified and each unused position contains a zero (0). The hyphen separating the year and the serial number in LC printed products is not carried in the MARC record. For example, the serial number in control number 85-2 is carried as 85000002.

Supplement number: (LCCN structure A only)

This character position was originally defined to carry a supplement number for dashed-on supplement entries in bibliographic records. No specific use of supplement numbers was ever implemented for authority records, thus, LC uses a blank (#) in this position.