Related: The Collection, Tutorials

All About Call Numbers: Library of Congress


Ever had trouble finding a book in the library because you couldn’t figure out the call number? If so, you’re not alone. Call numbers tell us where a book should go and are useful for organizing a library collection, but for many library customers they take getting used to.

TIP: You may have also noticed that some of Trinity’s call numbers start with numbers, while some of them start with letters. What’s going on? The reason we have two kinds of call numbers is that we’re in the process of switching from the Dewey Decimal system to the Library of Congress system. Some day soon all of the call numbers will match. What a relief!

This week, we’re going to talk about call numbers that start with letters. These are called Library of Congress call numbers because they follow the same scheme as the Library of Congress (or LOC). LOC call numbers look something like this:


Here’s what an LOC call number means and how it works:

Start at the top and work your way down.

The first line, HV, is the class and subclass — meaning, it tells you broadly what the book is about. In this case, the class (H) is Social Sciences and the subclass (HV) is Social Pathology, Social and Public Welfare, and Criminology. So this book is about one of those subtopics. (Visit the Library of Congress for a guide to classes and subclasses.)

TIP: Books are organized alphabetically by their class and subclass: HA before HB, HB before HC; L before M, M before N; etc.

The second line is the classification number (40.54), which narrows down the topic and makes sure that books on the same topic will be near each other. For instance, if HV 40.54 .L43 2010 is about social work administration and leadership, HV 40.54 .R6 and HV 40.54 .T7 should be, too — since they all have the same class, subclass, and classification number.

TIP: Classification numbers are arranged in order like any decimal number: 40.54 before 40.56; 41 before 45; etc.

The third line is called a “Cutter Number” (.L43) and is used to further organize books within a particular topic. It may represent the author (e.g. .K3 for Kelly), geographic region (e.g. .K8 for Kyrgyzstan), or other aspect of the material.

TIP: Cutter Numbers are where call numbers get tricky: they are put in order like decimals even though they look like whole numbers — meaning .L43 goes before .L5, while .L429 goes before .L43.

The last line is the year of publication (2010). The year is organized chronologically and helps distinguish between different editions of the same book.

Visit the Kent State website for a useful tutorial on LOC call numbers, test your skills with these practice exercises, or play Carnegie Mellon’s online shelving games.

TIP: Call numbers organize books by topic and subtopic, which means that if you find one book you like, there should be other similar works nearby. The next time you’re doing research, try finding just one or two call numbers, then browsing the shelf in that area for more books on your topic!

TIP: Some of our call numbers start with the letter J but are not actually LOC call numbers. If you see the letter J by itself at the beginning of a call number (e.g. J 341.5 or J HV 209.6) you are looking at a juvenile book. These books are found in our juvenile collection on the 1st floor and are organized by the remainder of their call numbers.

TIP: A basic understanding of call numbers should make it easier to find the materials you need. But even if you are a call number expert, we ask that you not put books back on the shelves once you’ve taken them down. Put them on one of the many tables and book carts found throughout the library, instead. This helps the librarians be sure that our books are being reshelved with 100% accuracy. The more accurate we can be, the easier it will be to find things the next time you need them!

Stay tuned for a future post on Dewey Decimal call numbers, and become a master of the library collection!

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