Books in the Howard-Tilton Library are organized using the Library of Congress Classification System.
| Call number | Floor |
| A - DA | 4 |
| DB - M | 3 |
| N - QD | 2 |
| QE - Z | 1 |
The first letters in call numbers are associated with subject areas.
| Letter | Subject area |
|---|---|
| A | General Works |
| B | Philosophy, Psychology, and Religion |
| C | Auxiliary Sciences of History |
| D | General and Old World History |
| E | History of America |
| F | History of the United States and British, Dutch, French, and Latin America |
| G | Geography, Anthropology, and 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, and General Information Resources |
