010 Library of Congress Control Number

Library of Congress control numbers (also know as LCCNs and previously as LC card numbers) were first issued in 1898. They are assigned by the Library of Congress, often as part of the PCN program.

Since December 2000, LCCNs consist of a two-character prefix (often containing blanks), a four-digit year, and a six-digit serial number. Prior to January 2001 these numbers had a three-character prefix (often containing blanks), a two-digit year, a six-digit serial number, and a trailing blank. The number was often, but not always, displayed with a hyphen separating the year and the serial number. Numerous examples of the old and new formats are given in BF&S).

The LCCN--when there is one--is found in the 010 tag of the MARC record. This is a simple tag for which there are no defined indicators. There are four valid subfields, but only two of them occur with any frequency. 

Subfield a contains the full LCCN. This is a non-repeatable subfield (in a non-repeatable tag) which is fine because a book can only have one valid LCCN. That brings us to subfield z (the other one you will come across) which contains cancelled/invalid LC Control Numbers. Subfield z is repeatable (because mistakes often happen in multiples and this is a subfield where mistakes are kept track of).

 If one of the following conditions exists, the LCCN is invalid:

• The item is a new edition but is printed with the LCCN of a previous edition.
• The item is cataloged separately but is printed with the LCCN of the multipart monograph or series of which it is a part.
• The printed LCCN has an obvious typographical error (e.g., the printed LCCN differs from the LCCN found in the LC catalog), but the LCCN is still structurally correct (e.g., a two- or four-digit year followed by a serial number of up to six digits).
• LC used the same LCCN in a record for a different item.

Subfield z is also used when the accuracy of the LCCN is in doubt by the cataloger or to record the LCCN of former LC or CONSER records when they are deleted because of record merging.