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Guide to Dewey Decimal Classification

The books in the library are arranged on the shelves using the Dewey Decimal Classification (DDC). It is the most widely used library classification system in the world. The word “Dewey” refers to Melvil Dewey (1851-1931) who devised the classification, and was first published in 1876. The second word “Decimal” refers to the base-ten notation that is used to denote and relate subjects. It uses Arabic numerals treated like decimal fractions. Hence the name of the classification is the Dewey Decimal Classification. It is continuously revised to keep pace with knowledge and is currently on edition 23.


In the Main library, or James Hardiman Library, the collection is spread over three floors. On the podium or ground floor level you'll find the Law collection, Official Publications, European Documentation Collection, and General Reference books, as well as our Atlas and Map Collections. On the first floor you'll find Arts, Humanities, Social Sciences and Business. On the second floor, you'll find material relating to Computer Science, Engineering, Science and some Medical books. Each of the floor plans indicates where particular Dewey numbers are located.


Towards the back of the Law area across a bridge, the Nursing and Midwifery Library is located. In the Clinical Sciences Institute at University College Hospital, Galway, you'll find the Medical Library.


Within each of these areas of the Library, the books are shelved by classification number. The classification number (also called the class number or shelf number) appears on a label on the spine of the book. It is made up of the Dewey number and the first three letters of the author's surname or the first three letters of the title, whichever is the main entry on the catalogue. Books are placed on the shelf in increasing numerical order of the Dewey number. When two books have the same Dewey number they are arranged in alphabetical order of the first three letters from the author's name, or, first three letters from the title of the book. The end of each row of shelves indicates the numbers contained in those shelves.


The Library Catalogue will tell you the exact Dewey number of each book. By clicking on the Dewey number a floor plan will be displayed showing you where in the Library to find books at this number.

Main Classes

  • 000 Computer science, information & general works
  • 100 Philosophy & psychology
  • 200 Religion
  • 300 Social sciences
  • 400 Language
  • 500 Science
  • 600 Technology
  • 700 Arts & recreation
  • 800 Literature
  • 900 History & geography

Dewey is further divided into 10 branches that are called divisions

000 Generalities

000 is the most general class, and is used for works not limited to any one specific discipline, e.g., encyclopaedias, newspapers, general periodicals. This class is also used for certain specialized disciplines that deal with knowledge and information, e.g., computer science, library and information science, journalism. Each of the other main classes (100–900) comprises a major discipline or group of related disciplines.


010 Bibliographies

020 Library & information sciences

030 Encyclopaedias & books of facts

040 [Unassigned]

050 Magazines, journals & serials

060 Associations, organizations & museums

070 News media, journalism & publishing

080 Quotations

090 Manuscripts & rare books

100 Philosophy & psychology

100 covers philosophy, parapsychology and occultism, and psychology.


110 Metaphysics

120 Epistemology

130 Parapsychology & occultism

140 Philosophical schools of thought

150 Psychology

160 Philosophical logic

170 Ethics

180 Ancient, medieval & eastern philosophy

190 Modern western philosophy

200 Religion

200 is devoted to Religion.


210 Philosophy & theory of religion

220 The Bible

230 Christianity

240 Christian practice & observance

250 Christian pastoral practice & religious orders

260 Christian organization, social work & worship

270 History of Christianity

280 Christianity denominations

290 Other religions

300 Social sciences

300 cover the social sciences. It includes sociology, anthropology, statistics, political science, economics, law, public administration, social problems and services, education, commerce, communications, transportation, and customs.

310 Statistics

320 Political science

330 Economics

340 Law

350 Public administration & military science

360 Social problems & social services

370 Education

380 Commerce, communications & transportation

390 Customs, etiquette & folklore

400 Language

400 comprise language, linguistics, and specific languages.


410 Linguistics

420 English & Old English languages

430 German & related languages

440 French & related languages

450 Italian, Romanian & related languages

460 Spanish, Portuguese, Galician

470 Latin & Italic languages

480 Classical & modern Greek languages

490 Other languages

500 Natural Sciences & Mathematics

500 cover the natural sciences and mathematics.


510 Mathematics

520 Astronomy

530 Physics

540 Chemistry

550 Earth sciences & geology

560 Fossils & prehistoric life

570 Biology

580 Plants (Botany)

590 Animals (Zoology)

600 Technology (Applied sciences)

600 is Technology.


610 Medicine & health

630 Engineering

630 Agriculture

650 Management & public relations

660 Chemical engineering

670 Manufacturing

680 Manufacturing for specific uses

690 Construction of buildings

700 The Arts

700 covers the arts: art in general, fine and decorative arts, music, and the
Performing arts. Recreation, including sports and games, is also classed in 700.


710 Arts, planning & landscape architecture

720 Architecture

730 Sculpture, ceramics & metalwork

740 Graphic arts & decorative arts

750 Painting

760 Printmaking & prints

770 Photography, computer art, film, video

780 Music

790 Sports, games & entertainment

800 Literature & Rhetoric

Class 800 covers literature, and includes rhetoric, prose, poetry, drama, etc.


810 American literature in English

820 English & Old English literatures

830 German & related literatures

840 French & related literatures

850 Italian, Romanian & related literatures

860 Spanish, Portuguese, Galician literatures

870 Latin & Italic literatures

880 Classical & modern Greek literatures

890 Other literatures

900 Geography & History

Class 900 is devoted primarily to history and geography. It also includes biography and genealogy.


910 Geography & travel

920 Biography & genealogy

930 History of ancient world (to ca. 499)

940 History of Europe

950 History of Asia

960 History of Africa

970 History of North America

980 History of South America

990 History of other areas


NOTE: Some deviations from above are used by James Hardiman Library, notably 490 for Irish language and 828.99 for Anglo-Irish literature. Please consult the catalogue for more details.


Have you ever wondered how the numbers are built? Hierarchy in Dewey Decimal Classification is expressed through structure and notation. Notational hierarchy is expressed by length of notation.

See the following example:
300 Social Sciences
330 Economics
332 Financial economics
332.4 Money
332.41 Value of money
332.414 Factors affecting fluctuations in value
332.4142 Devaluation

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