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Understanding Call Numbers

last modified 2010-08-23 01:45 PM

Library of Congress Classification System.

Understanding Call Numbers and Locating Books 

Our library, like many academic libraries, uses the Library of Congress Classification System to organize library materials. When books are cataloged, they are assigned a call number. These call numbers are like addresses, telling you where to find the book in the library.

Call numbers use a combination of letters and numbers to arrange books according to subject. The Library of Congress Classification System divides areas of knowledge into 21 main classes, assigning letters to each class. For example, the letter K is assigned to Law, so books about Law will be found in the K section of the library. The 21 main classes are further subdivided into specific subject areas, which have also been assigned alpha or numeric codes. Additional codes indicating information about the author and publication year are added to the subject code and you have a call number.

You just need to remember that books are shelved according to subject and that call numbers tell you where to find the exact book on the shelf. Read more about how the Library of Congress system works.

Reading Call Numbers

Let's take a look at how call numbers are composed. Read the call number line by line, top to bottom. This is how the call number will appear on the spine of the book. Note that in the catalog, the call number will usually be displayed as one line: PR 2848 .W47 2007. The call number is the same, whether written in four lines on the side of a book or in one line in the catalog.





  General Subject

  Specific Subject


  Edition date

  • Read the first line in alphabetical order. (PR comes before PS on the shelf.)
  • Read the second line as a whole number. (PR 2848 is located after PR 2846.)
  • Read the third line alphabetically, then by decimal number. (.W47 comes before .Y35; .W47 comes after .W235--remember that as a decimal, .47 is larger than .235)
  • Read the fourth line as a whole number; it is the publication year of the item.  

Identifying the Collection

Before you go to the shelves to look for your book, first determine in which part of the collection the book is located. If you have done a catalog search in iBistro (the MLC Library catalog), check the Holdings at the bottom of of the display for the call number, copies, material type, and location. Most of our books are located in the Main (On Shelf) Collection, meaning they can be found on the lower level.  For a visual view take a look at the Library Map.

Other MLC collections use the same call number system, but are located in different parts of the library. The Holdings detailed display will tell you in which collection the item is found. Collections include:

  •  AV Room (located on the uper level by library offices)
  • Children's Literature (located on the upper level)
  • Curriculum Materials (located on the lower level)
  • Current Magazines (located on the upper level)  
  • Magazine Bound (located on the lower level)
  • Main (On Shelf) Collection (located on lower level)
  • Microfiche Catalog (located on the upper level in the AV Room)
  • Music Scores and Studies (located on the lower level)
  • Oversize (located on the lower level)
  • Rare Books (located in the library office on the upper level)
  • Reference (located on the upper level)
  • Special Collections (located on the upper level in Reference)


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