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Library of Congress Classifications: LC System

This LibGuide describes Library of Congress call numbers and how books are arranged on the shelves using this system.

LC System

The Library of Congress system is used by most college and university libraries to organize books on the library shelves.  It is an alpha-numeric system. Books are arranged in the library according to their subject. Because it would be impossible to describe the subject in words on the spine of each book, libraries use codes for these subjects. These codes are called "call numbers," and the system of call numbers is called a "classification scheme." Each item in the library has a label with letters and numbers (together called a call number) which indicates its place on the shelf. The letters indicate a subject area and the numbers which follow further subdivide the broader topic into more specific categories. 

Both physical and online books are organized using the Library of Congress Classification. Knowing the classification scheme can help you when you are doing research for books in the library.   

Some libraries (especially public libraries) use the Dewey Decimal classification scheme. At APU Libraries (as in many academic libraries) we use the Library of Congress Classification scheme, or LC for short. For detailed information about LC classes and subclasses, see the Library of Congress Classification Outline below. 


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Denise R. Gehring, MSLIS, MA
Associate Professor;
Head of Collections & Technical Services
Librarian for the School of Nursing, Public Health, & ALCI (ESL)
Hugh & Hazel Darling Library #210
701 E. Foothill Blvd., PO Box 7000
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Library of Congress Classification Outline

The following information is from the Library of Congress website that includes a list of the classifications by subject. 

Listed below are the letters and titles of the main classes of the Library of Congress Classification. Click on any class to view an outline of its subclasses (

The files below are available for downloading in PDF (the first link in each line), WordPerfect format (noted as WP version), and in Word format (noted as Word version).

How to Read a Call Number

When you find a Library of Congress (LC) call number in your library search, notice that it is written a bit differently than it will appear on the book spine. In the database, it reads straight across. However, on the book spine, it will be broken down into components that make it easier to read.

  • Books are arranged alphabetically. The first letter of an LC call number indicates the general class the call number falls within.
  • Numbers follow the letters. The numbers define the subject of the book.
  • The Cutter Number is the next set of numbers, and it further distinguishes the book. The Cutter Number indicates the author or title of the book.
  • The edition of a volume is the next part of the call number. The year of publication follows the Cutter number to indicate the edition

(Image from the online library learning centern)

Here is an example from the library catalog:

(Images are from the Washington State University Library)

Library of Congress Classification System

The following short video clips will help you understand how the library of congress classification and how you can use it to locate books in the library: