000 General knowledge
100 Philosophy, paranormal phenomena, psychology
200 Religion
300 Social sciences
400 Language
500 Natural sciences and mathematics
600 Technology (Applied science)
700 The arts. Fine arts and decorative arts
800 Literature and rhetoric
900 Geography and history
Each main class has ten divisions, for example:
300 Social sciences
310 Statistics
320 Political science
330 Economcs
340 Law
etc.
Each division in turn breaks down into ten sections, for instance:
340 Law
341 International law
342 Constitutional and administrative law
343 Law in military affairs, defence, public property, finance, taxation, commerce and industry
etc.
The first three numbers may be followed by a full stop, and then by other numbers describing the subject of the book more specifically:
341.2422 International Law. European Union