The Dewey Decimal System groups books by subject matter. The main divisions are 10 main classes, with each class covering a different topic. These classes are:
000-099 General works
100-199 Philosophy and psychology
200-299 Religion
300-399 Social sciences
400-499 Language
500-599 Pure science
600-699 Technology
700-799 Arts and recreation
800-899 Literature
900-999 History and Geography
Within each class, books are further divided into 10 divisions, and then into 100 sections. For example, in the 500 class for pure science, the first division is mathematics (500), and the second division is earth and astronomy (550). Each division is then divided into 100 sections, so the section for earth and astronomy would be 550.01-550.99.
