The basic control number has been fixed in length at 12 characters used.  The prefix, year, and serial number are the basic elements required to make an LCCN unique.

LCCN Structure

Name of element

Number of characters

Character position in field

Alphabetic prefix






Serial number



Alphabetic prefix:

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 unused positions contain blanks (#).  If no prefix is present, the prefix portion contains blanks.


010  ##  $a##2001045944


For control numbers assigned under the LCCN structure, the year portion consists of four digits.  In most numbers, the year portion reflects the year in which the LC control number was assigned to the record.

Serial number:

The serial number portion consists of one to six digits.  Serial numbers of less than six digits are right justified and unused positions contain zeros.  The hyphen which separates the year and the serial number on LC printed products is not carried in the MARC record.  For example, the number 2001-2 is carried as 2001000002 in a record.

To return, select:

010  Library of Congress Control Number