Library of Congress Classification Overview


Call Number: the unique combination of letters and numbers, or just numbers, that indicates the position of the book on the shelf. At Yale, books cataloged before about 1970 have call numbers based on various iterations of the local Yale classification ("Old Yale"). Most books cataloged from 1970 on have call numbers based on the Library of Congress (LC) classification scheme. In most Yale locations, call numbers using LC classification generally are identified by "(LC)" in the last line of the call number.

Call numbers based on LC include both a classification number (class number) and a cutter number. The classification number refers to the subject of the book. If a single cutter number is used, the cutter number refers to the main entry of the work (the author or, if title main entry is used, the title). If there are two cutters, the first cutter is used to bring out a more precise aspect of the subject and the second cutter usually refers to the main entry of the work. (For common exceptions, see Examples 5-7)

LC call numbers generally use a mixed notation of one, two, or three CAPITAL letters, integral or whole numbers from 1 to 9999 with possible decimal extensions, one or two cutter numbers, and, if appropriate, a year of publication.

A single letter, always combined with numbers, represents a main class, corresponding roughly to a broad academic discipline, e.g. N33=general dictionaries of the visual arts.

Double or triple capital letters combined with numbers represent subclasses of the main class, e.g. NB50=dictionaries & encyclopedias of sculpture, i.e., a subclass of the broader visual arts. (In contrast, Old Yale notation may include lower case letters)

On MARC records the LC call number is recorded in the 050 field:

  • LC call numbers assigned by the Library of Congress are tagged as 050 00 or 050 _0.
  • LC classification call numbers assigned by libraries other than the Library of Congress are tagged either 050 _4 or 050 14.
  • National Library of Canada call numbers in field 055 are sometimes in synch with LC classification and sometimes not; copy catalogers should not consider them to be equivalent to LC classification call numbers
  • On OCLC records field 090 is sometimes used for recording a locally assigned LC classification call number. CAUTION: A call number appearing in 090 in Voyager is not necessarily LC classification. The call number must be evaluated by searching it against the Orbis OPAC in the call number index. If the 090 is judged to be LC classification, it is generally retagged to 050 _4 (if it does not interfere with workflow). When in doubt, the copy cataloger should check the number on ClassWeb (if authorized) or with a catalog librarian.