Hello Latasha! 

The Dewey Decimal Classification System is a library classification system first published in the U.S. by Melville Dewey in 1876.

It consists 20 main classes:
000-099     General Works
100-299     Philosophy, Psychology and Logic
200-399     Religion
300-499     Social Sciences
400-599     Natural Sciences
500-699     Technology and Applied Sciences
600-799     Fine Arts and Recreation
700-899     Literature
800-999     History and Biographies