Dewey Decimal Classification

The main Dewey Decimal classes are:

000 Generalities 
100 Philosophy and psychology 
200 Religion 
300 Social Sciences 
400 Language 
500 Natural sciences and mathematics 
600 Technology (Applied sciences) 
700 The arts (fine and decorative) 
800 Literature and rhetoric 
900 Geography and history

Each class is further subdivided at the hundred divisions and the the thousand sections. Numbers are placed after a decimal point to further identify material more specifically by subject.