The University of Delaware Library uses the Library of Congress classification system to organize most materials. Each book (or bound volume of a periodical) is assigned a call number - a unique number that specifically identifies one copy of one book. A book is shelved according to its call number. Therefore, the call number also serves as a book's address or location in the building. The Library of Congress classification system groups books on the same subject together on the shelves.

A call number is always read line-by-line, from top to bottom. Library of Congress call numbers always start with letters - typically one or two letters, sometimes three.

Above is an example of call numbers in order, as you might see them on the spines of books on the shelves:

At the University of Delaware Library, the first letter of the call number is used to indicate the floor on which items with that call number are shelved. Special locations may be listed before the call number (see examples below).