Most items in our Library are arranged using Library of Congress (LC) call numbers. Call numbers are a method to keep items in order and group them by subject. An LC call number consists of a series of letters and numbers. An item's call number is indicated in the library catalogue, and physically located on the spine of each item. {catalogue screenshot, showing call #, picture of row of books with call number highlighted}

LC Classification 

In the Library of Congress (LC) Classification System, each item is assigned a unique call number based on its main focus or subject. Since call numbers are based on the main subject of the item, items on the same topic are shelved together.  

All LC call numbers begin with letters that represent broad subject areas:

LC Classification: Main Subject Classes

A: General Works  
B: Philosophy, Psychology, Religion  
C: Auxiliary Sciences of History, such as Archeology, Genealogy, Biography
D: World History
E & F: History of the Americas
G: Geography, Anthropology, Recreation  
H: Social Sciences
J  Political Science
K: Law  
L: Education
M: Music  
N: Fine Arts 
P: Language and Literature  
Q: Science  
R: Medicine  
S: Agriculture  
T: Technology  
U: Military Science  
V: Naval Science  
Z: Bibliography, Library Science, Information Resources

These broad subjects are narrowed further by the addition of a second letter, called a subdivision. For the full listing of the main subjects (classes) and their subdivisions, see the Library of Congress site.

How to Read a Call Number

Let’s start with a sample call number:  QL737.M336 O83 2004

This call number will lead you to a book with the title Tasmanian Tiger, by David Owen.

The first letter, "Q" represents one of the main subject classes listed above.  In this case, the main subject is Science. Items are shelved by this letter first, in alphabetical order.

The second letter "L" represents a subdivision of the sciences, Zoology. On the shelf, books with the subdivision of QL would be in the "Q" section, and then arranged alphabetically within that Q section  (QL books would be shelved after any QK books we own, and so on).

The numbers following the letters are classification numbers (in this example the numbers "737").  In combination with the class and subdivision, the classification number further narrows the subject matter.  These are read as whole numbers, so "QL737" would come after "QL700" but before "QL800."

The next piece of information, the "M336," is called a "cutter" number. The letter part of the cutter is read alphabetically. However, the numeric component of a cutter number is always read as a decimal, so in this case "M336" is really read as "M.336," and "M336" would come after "M3" but before "M4."  

If necessary, a second cutter may be included in a call number, also (in this case, the second cutter is "O83").  It is read in the same way as the first cutter, as a way to further narrow down the location of the book on the shelf.

Following the cutter number(s) you often will see the year of publication. In this case, that would be 2004.

Browse the Shelves

Sometimes, you may have a topic in mind but not know a specific title. In these cases, it's useful to browse the shelves in the general subject area you're interested in. You may find it useful to refer to the LC classification website to discover the general call number area you should browse, or look at the signs posted on the ends of our shelves, which describe some of the subjects you'll find in each aisle.

Once you find a book or section that is relevant to your topic, it's often worthwhile browsing the surrounding shelves to discover even more books related to your topic.