Rensselaer Libraries

Almost all materials (i.e. books, journals, audio cassettes, videotapes, and microfilm) housed in a library are assigned call numbers.

• Call numbers identify an item's subject and location in a library.
• Call numbers are assigned to items based on a classification scheme. Library materials on similar topics will have similar call numbers and will be shelved together.
• There are three major classification systems used by most libraries in the United States--Library of Congress Classification System (LC), Dewey Decimal Classification System (DDC), and the Superintendent of Documents System (SuDocs).
• Rensselaer Research Libraries use all three of these systems. More information is provided on each of these systems below.

1. The Library of Congress (LC) classification system is used to catalog our books. This system is used to assign call numbers to and shelve books in the Reference Area and Book Stacks. The LC system divides materials into 21 different subject areas. An LC call number consists of one or two (or rarely three) letters followed by a number. The initial letter or letters indicates the general subject of the book. The following guides provide additional information on this system:

Library of Congress Classification Outline, a guide to the subject organization by letter(s) from the Library of Congress
Understanding Library of Congress Call Numbers, a guide produced by the American Museum of Natural History
Popular Subjects and Their Library of Congress Call Numbers, a subject guide to the LC system from Boston Public Library

2. The Dewey Decimal classification (DDC) system is used to catalog our journals and magazines. This system is used to assign call numbers to and shelve books in the Journal Stacks and Journal Microfilm collections. DDC is often used in public libraries or K-12 school libraries. The system divides materials into ten major classes which are further subdivided into subclasses. Decimals are used for further subdivisions. The following guide provides additional information on this system:

Outline of the Dewey Decimal System, a guide to the subject organization by category from Duke University Libraries
How the Dewey Decimal System Works, a more detailed explanation of the system, also from Duke University Libraries

3. The Superintendent of Documents Classification System (SuDocs) is used to organize our federal government documents. This system is used to assign call numbers to and shelve books in the US Doc Stacks and US Doc Microfilm collections. SuDocs was created by the U.S. Superintendent of Documents to classify government documents according to the government agency which published them. A SuDocs number begins with a one, two or three-letter code indicating a U.S. government agency. For example, A for Department of Agriculture, ED for Department of Education, and T for the Treasury Department. This letter is followed by a number indicating the sub-agency which issued the publication. This is followed by a colon, then a letter/number combination identifying the individual title, volume, year or issue number. The following guide provides additional information on this system:

Explanation of the Superintendent of Documents Classification Scheme, a guide to the agency designations, from Illinois Institute of Technology.
Finding a Document on the Shelf, a more detailed guide to the SuDoc numbering system, from the Federal Library Depository Program.

Our web page, Location/Call Number Guide, will direct you to library materials and provide floor plans to locate collections.