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Understanding Call Numbers

The MLC Library uses the Library of Congress classification system to organize our collections. Understanding the LC System makes finding books and media a little easier for the patron.

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 arranged 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.

Remember, 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 .A2 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 .W23--remember that as a decimal, .47 is larger than .23)
  • 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 book search in the MLC Online Catalog, check out the Location in the Call Number/Item display.


    Most of our books are located On shelf, meaning they can be found on the lower level.


    Other library collections use the same call number system, but are located in different parts of the library. The Call Number/ Item display will tell you in which collection the book is found. Collections include:

    • On shelf (located on lower level)
    • Reference (located on the upper level)
    • Main Collection (located on lower level)
    • Oversize (located on the lower level)
    • Current Periodical (located near the newspapers on the upper level)
    • AV Room (located on the upper level by library offices)
    • Children's Literature (located on the upper level)
    • Music Scores and Studies (located on the lower level)
    • Periodical Holdings (located on the lower level)
    • Rare Books (located in the library office on the upper level)
    • Curriculum Room (located on the lower level)
    • Star Books Room (located on the lower level)

    Finding Books on the Shelf

    Once you have determined which collection your item is located, start by looking for the signage of the section that corresponds to the beginning of the call number. This signage gives the range of call numbers found on each side of the shelves. For example, for the call number PS 234 .A2 W47 2007, go to the PS section. Look at the shelf end cape signage on the sides of the stacks. Next, look in the PS section for the whole number 234. The signage on the sides of the shelves will direct you to the correct row. For example, if the signage on the side of the stack looks like this:

    Location of books.

    the book will be located somewhere in this row of shelves, because PS 234 falls in between PS 228 and PS 648. Use the rest of the call number to locate the book.


    Remember that books are shelved according to subject, which means that you will find similar books on your research topic near each other. When you find a book that fits your research topic, take a look at the other books nearby. You might end up with a few more sources!

    Maps of the Upper and Lower levels of the library.