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Call Numbers: Overview

Learn how books are organized and labeled at Northwestern University Library

Call Numbers at NUL

Have you ever wondered how library books are assigned their places on the shelves? Have you ever wondered if call numbers mean anything about the book?  Did you know that the library uses multiple types of call numbers? This libguide will provide an introduction to understanding and using library call numbers.

What are call numbers?

Each book in the library has a unique call number. A call number is like an address: it tells us where the book is located in the library.  Call numbers appear on the spines of books and journals and in the library's catalog.  Note that the same call number can be written from top-to-bottom, or left-to-right.

What do call numbers mean?

Besides the materials in Government Information, the call numbers used by the library are  classified by subject, so you can often find several helpful books on the same shelf, or nearby.

The first sections of the call number represent the subject of the book. The letter-and-decimal section of the call number typically represents the author's last name. The last section of a call number is often the date of publication.

What type of call numbers are used at Northwestern University Library? 

The library uses 3 different types of classification schemes to organize various collections and libraries.

  • Library of Congress - Used exclusively in our Music and Transportation libraries.  At the beginning of 2015, all new acquisitions will have a Library of Congress call number.
  • Dewey Decimal - Until 2015, the majority of the library's collection was classified using Dewey Decimal call numbers.
  • SuDocs (Superintendent of Documents Classification) - SuDocs call numbers are issued by the United States Government Printing Office for items published by the U. S. Government. The SuDocs Classification System is not a subject based system, instead items are arranged by the department or the agency issuing the publication, such as the FBI or the Department of Health. As a Depository for Government Documents, Northwestern University Library uses the SuDocs Classification System for all government documents.

I thought Northwestern University Library only used Dewey call numbers?  

For many years, the main library collection were classified with Dewey Decimal call numbers but specific collections have used Library of Congress (LC) numbers exclusively. Starting in 2015, the library will give all newly acquired materials a Library of Congress call number.  To find out more information about why we are making that change and where those books will be located, please refer to our FAQ. 


Ivan Albertson
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Northwestern University Library
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