The Library of Congress Classification System
ESF 200—Information Literacy

I. Purpose of the L.C. Classification System:

Materials in a library are physically organized by subject so that they may be found easily. The Library of Congress Classification system, used in most college, university and research libraries (including Moon and SU libraries), uses a series of letters and numbers to designate specific subjects. This groups books on the shelf by subject and provides a location or address for each book.

II. Components of the L.C. Classification System:

The L.C. call number consists of two principal elements: a class number and book number to which symbols may or may not be added designating a particular title or edition.

1. The class number is composed of a letter or combination of letters which designates the divisions and subdivisions of a main subject and number or numbers ranging from 1 to 9999 which may be extended decimally.
   
   Examples:
   

   Q	Science in General
   Q	125 History of Science
   QD	Chemistry
   QH	Natural History including Biology
   QK	Botany
   QK	641 Plant Anatomy
   QL	Zoology
   QP	Physiology including Animal Biochemistry
   QR	Microbiology
   S	Agriculture
   S	590 Soils
   SD	Forestry
   SD	Silviculture

2. The book number (or author number) consists of a letter
   of the alphabet and a decimal number. The book number has
   the effect of placing books alphabetically by author
   within an L.C. Classification.
   
   Examples: .A9 B34 C34 .C4 .F58 P61 .P7 U58 U9 (NOTE: In some book numbers the dot, point or decimal point is not indicated. Whether or not it appears the number is treated decimally). (over) Occasionally in some L.C. call numbers the book numbers are used for a subdivision of the class number: Example: Brown, Herbert Charles, Boranes in Inorganic Chemistry QD Inorganic Chemistry 181 Special Elements B1 Boran (Subdivision of the class number) B73 Book number (for author Brown)

III. Additional Information in the Call Number:

1. Publication date of the book. Dates are then shelved in chronological order:
   
   Examples:
   

   S	S
   591	591
   A24	A24
   1964	1972

2. A copy number is given when the library owns more than one copy of the same book.
   
   Examples:
   

   S	S	S
   591	591	591
   A24	A24	A24
   1972	1972	1972
   	C.2	C.3

IV. Arrangement on the Shelves:

1. Books are arranged first by class number and then by book numbers. Class numbers are arranged alphabetically and numerically:

   HD	HD	Q	QK	QK	S	SF	SH	SH	TD
   996	9868	150	85.5	85.7	120	31	377	377	10

2. Book numbers (author numbers) are arranged decimally, regardless of whether a decimal appears in the number.

   QK	QK	QK	QK	QK	QK	QK	QK
   85.5	85.5	85.5	85.5	85.5	85.5	85.5	85.5
   A35	B55	B6	M46	O3	O315	R55	R8