In 1876 the American librarian Melvil Dewey published "A Classification and Subject Index for Cataloging and Arranging the Books and Pamphlets of a Library." In it he outlined a new system of arranging the contents of a library, a system that today we call the Dewey Decimal System. Dewey's system is based on the division of all knowledge into 10 groups:

000 Generalities
100 Philosophy
200 Religion
300 Social sciences
400 Language
500 Natural sciences & mathematics
600 Technology (Applied sciences)
700 The Arts
800 Literature & rhetoric
900 Geography & history

These general categories are further subdivided into more specific topics. For example, the book Teleworking has the call number: 331.25 T269 1998

331.25 T269 1998
300 - Social Sciences
330 - Economics
331 - Labor Economics
331.2 - Compensation and other conditions of employment
331.25 - Including telecommuting