The University of Delaware uses the Library of Congress Classification System, which groups books together by subject. The different subjects are given a corresponding letter. Here's how it works:
DS35.3-DS326: History of Islamic world, Arab and Middle Eastern countries
DT: History of Africa
HQ: Women's rights
JQ1758-JQ1852: Political science (Middle East)
KBP: Islamic law
PJ: Arabic language, linguistics and literature
This is just a sampling of the subjects that you might encounter. Because Islamic Studies is so interdisciplinary, you may need to do a specific subject search in DELCAT Discovery, the library's catalog, to find the call number for the book that you need. Once you find a call number range that looks promising, try browsing the stacks to see if you might find other books that fit your topic.
For more information about how to locate a book in the library using a call number, please see the ENGL110 class page on Finding Books.