Many academic libraries in the United States use the Library of Congress Classification for call numbers. This system uses a combination of letters and numbers to arrange materials by subject on the shelves ("the stacks")  of a library.

The LCC System is preferred for academic collections because the call number, being alphanumeric, can be shorter and more descriptive than by using numeric systems like Dewey Decimal, used by public libraries.

A -- GENERAL WORKS

B -- PHILOSOPHY. PSYCHOLOGY. RELIGION

C -- AUXILIARY SCIENCES OF HISTORY

D -- WORLD HISTORY AND HISTORY OF EUROPE, ASIA, AFRICA, AUSTRALIA,  ETC.

E -- HISTORY OF THE AMERICAS

F -- HISTORY OF THE AMERICAS

G -- GEOGRAPHY. ANTHROPOLOGY. RECREATION

H -- SOCIAL SCIENCES

J -- POLITICAL SCIENCE

K -- LAW

L -- EDUCATION

M -- MUSIC AND BOOKS ON 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. INFORMATION RESOURCES (GENERAL)