Understanding Call Numbers What are call numbers for? Each book in the library has a unique call number. A call number is like an address: it tells us where the book is located in the library.  Call numbers appear  Note that the same call number can be written from top-to-bottom, or left-to-right.  Prescott Memorial Library , like many academic libraries in the U.S., uses Library of Congress Classification for call numbers. This system uses a combination of letters and numbers to arrange materials by subjects. Reading Call Numbers Putting Call Numbers in Shelf Order To understand how call numbers are put in order in Library of Congress Classification, again look at each section of the call number. What does the call number mean? Remember that Library of Congress Classification arranges materials by subjects. The first sections of the call number represent the subject of the book. The letter-and-decimal section of the call number often represents the author's last name. And, as you probably recall, the last section of a call number is often the date of publication.  For example: Why is this important to know? Because books are classified by subject, you can often find several helpful books on the same shelf, or nearby. For example, within the same call number LB2395, there are other guides for college study. Since Library of Congress Classification arranges materials by subjects, knowing the letter(s) for your subject area gives you a place to start browsing the shelves.