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Call Numbers

Learn how books are organized and labeled at Northwestern University Library

Why is the library switching over to LC call numbers for new books/journals?

This change will:

  • Increase the speed with which we bring you new books
  • Bring us in line with research library standards
  • Create a more welcoming research environment for incoming faculty and researchers already familiar with LC
  • Improve library efficiencies and save resources
  • Better prepare undergraduates for library environments at other academic institutions

What is the difference between LC and Dewey Call numbers?

The Library of Congress Classification (LCC) system was developed at the turn of the 20th century and was specifically created to categorize books and other items held in the Library of Congress. It features 21 (I, O, W, X, and Y are not used)  subject categories with resources being identified by a combination of both letters and numbers. For example, books on education are identified with a call number that begins with the letter “L” and those on political science under “J.” The number of classes and numerous subclasses is not restricted. Specific topics and geographic areas are often represented by alphabetic Cutter lists.

The Dewey Decimal Classification (DDC) system was developed in 1876 as a means to organize all knowledge.  The DDC uses notation in Arabic numerals, well-defined categories, well-developed hierarchies, and a rich network of relationships among topics. The ten basic classes are organized by disciplines or fields of study.  Each main class is further divided into ten divisions, and each division into ten sections. Except for a few optional provisions, the DDC notation is strictly numeric.

From Library of Congress

If I have a Library of Congress Classification Number, how can I find out what the Dewey number should be? Or vice versa?

There are very few one-to-one relationships between LC and Dewey and they are scattered; most relationships are many-to-many.

Is there a crosswalk between Dewey and LC numbers?

How can I tell the difference between Dewey and LC numbers?

Dewey numbers start with numbers while LC numbers start with one or two letters.  Learn more from the previous pages on this Libguide.

The call numbers for oversized/large books start with "L" for Dewey call numbers, how will oversized/large books be marked with LC call numbers?

The word “Large” will appear on the spine label of the book as well as in the item record in the online catalog.  With Dewey, Folios were signified by “F,” the word “Folio” will now appear on the spine label of the book as well as in the item record in the online catalog.

Some Dewey call numbers start with "L" for large, how do I tell those apart from new books about Education that have LC call numbers that start with "L"?

Remember that our materials are organized by location and then by call number.  In the item record, any oversized/large books will be located in a “Large” location such as MAIN Large Books.

If the book is located in the MAIN Library, the call number looks like LA210. S65 1993 and it has something to do with Education, it will be found in the LC section in 4S. Almost no Education books have single-letter class "L". Most have a two-letter class, like "LA."

If the book is located in MAIN Large Books, the call number looks like L 810.8 S7414c and it doesn't have anything to do with Education, it will be found in the Large Dewey section of the Main Collection. 

Where did all the books go in 4South?

Low-use books or those that are now available online were transferred to Oak Grove Library Center.  Those books are still available to check out - they just need to be requested from Oak Grove through the library’s catalog.   Books with call numbers between 820 – 839 were consolidated to one half of the tower.

What is going to go on the empty shelves in 4South?

Starting in January 2015, the library will start using Library of Congress (LC) call numbers for newly acquired books.  New books for the library’s main collection will be shelved in 4South.

Are all the LC books going to be in 4South?

No.  Some of our collections such as Music and Transportation already use LC call numbers.  Each of our other distinctive collections like Art, Africana, Curriculum and others will have designated shelves for the newly acquired LC books in their current location. Information about the other locations is available on the public website.

Are you going to put LC call numbers on all the books?

Not at this time.  With over 6 million volumes in our collection, we don’t have the resources to reclassify the whole collection.

Is there more information about the change to LC call numbers?

We do have a FAQ on the public website that provide more details about the new call numbers.  The FAQ will be updated regularly.

I have more questions about the switch to LC call numbers, who can I contact?

Students and faculty can contact their subject specialist at the library or email Mike Perry (