In libraries, a classification system is used to systematically group together items that have similar characteristics. The classification assigned to library materials is known as the "call number". The first part of a call number is derived through a classification system. Materials are classified for basically two reasons: 1) to enable them to be found quickly and easily; and 2) to bring together on the shelf materials that deal with similar subjects. Libraries group or classify materials by subject as well as by format (for instance, video or audio), size (regular or oversize), circulation policy (reference, reserve, or circulating), or type (periodicals, government documents).

Knowing about call numbers is essential for finding materials because they are shelved in numerical and alphabetical order by call number. It will help you understand how information is organized in a library and improve the ability to do research. A call number is a unique number that combines an item's classification or class number (composed of both letters and numerals) as well as an author or title number (also composed of letters and numerals). The latter may be followed by a date indicating the item's year of publication. The call number thus indicates each item's major subject content and physical shelf location.

Subject classification enables materials dealing with similar subject matter to be grouped together. There are many classification systems, but libraries in the U.S. most often use two: most special**, college, and university libraries use the Library of Congress (LC) Classification System, and public and school libraries usually employ the Dewey Decimal System (DDC).  The second part of a call number, usually letters, represents the author’s last name. In biographies (921 in DDC) the second part represents the first letters of the the person the book is about so that all books about a person are shelved together.

 **Special libraries may include research, business, tribal or museum libraries with a narrow focus for its specialized patrons.

Library of Congress Classification System (LC) –used mostly in special, college and university libraries.

The LC Classification System, developed in 1897, divides knowledge into 21 broad subject classes and identifies each by single letters of the alphabet, A through Z. (Five letters--I, O, W, X, and Y--are not used.) Combinations of letters and numbers (alpha-numeric system) indicate subtopics within classes and subclasses. For a basic list of the LC subject headings, go to the Library of Congress website. 

Dewey Decimal Classification System (DDC) –used mostly in school and public libraries.

The Dewey Decimal Classification (DDC) was developed by Melvil Dewey and first published in 1876. DDC divides knowledge into ten subject areas and uses three digit numbers plus decimals to classify materials. It is universally used in school libraries.

You can find the DDC of a book by looking up the MARC (machine-readable cataloging) record on many of the electronic databases accessible through SLED. Another source is the CIP (cataloging in publication) information printed on the verso (back side) of the title page of the book itself. A summary of the DDC is reprinted on the next page.

Dewey Decimal Classification System (1)

000 - Generalities

• 010 - Bibliography
• 020 - Library & Information science
• 030 - General encyclopedic works
• 040 -
• 050 - General serials & indexes
• 060 - General organizations
• 070 - News media, journalism, publishing
• 080 - General collections
• 090 - Manuscripts & rare books

100 - Philosophy & psychology

• 110 - Metaphysics
• 120 - Epistemology, causation, humankind
• 130 - Paranormal phenomena
• 140 - Specific philosophical schools
• 150 - Psychology
• 160 - Logic
• 170 - Ethics
• 180 - Ancient, medieval philosophy
• 190 - Modern Western philosophy

200 - Religion

• 210 - Natural theology
• 220 - Bible
• 230 - Christian theology
• 240 - Christian moral ... theology
• 250 - Christian orders & local church
• 260 - Christian social theology
• 270 - Christian church history
• 280 - Christian denominations & sects
• 290 - Other & comparative religions

300 - Social Sciences

• 310 - General statistics
• 320 - Political science
• 330 - Economics
• 340 - Law
• 350 - Public administration
• 360 - Social services
• 370 - Education
• 380 - Commerce, communications
• 390 - Customs, etiquette, folklore

400 - Language

• 410 - Linguistics
• 420 - English & Old English
• 430 - Germanic languages
• 440 - Romance languages French
• 450 - Italian...
• 460 - panish & Portuguese languages
• 470 - Italic languages; Latin
• 480 - Hellenic languages; Classical Greek
• 490 - Other languages

500 - Natural Sciences and Mathematics

• 510 - Mathematics
• 520 - Astronomy
• 530 - Physics
• 540 - Chemistry
• 550 - Earth sciences
• 560 - Paleontology
• 570 - Life sciences
• 580 - Botanical sciences
• 590 - Zoological sciences

600 - Technology (Applied sciences)

• 610 - Medicine
• 620 - Engineering
• 630 - Agriculture
• 640 - Home economics & family living
• 650 - Management
• 660 - Chemical engineering
• 670 - Manufacturing
• 680 - Manufacture for specific uses
• 690 - Buildings

700 - The Arts

• 710 - Civic & landscape art
• 720 - Architecture
• 730 - Plastic arts Sculpture
• 740 - Drawing & decorative arts
• 750 - Painting & paintings
• 760 - Graphic arts; printmaking and prints
• 770 - Photography and photographs
• 780 - Music
• 790 - Recreational & performing arts

800 - Literature and rhetoric

• 810 - American literature
• 820 - English & Old English literature
• 830 - Literature of Germanic languages
• 840 - Literature of Romance languages
• 850 - Italian...
• 860 - Spanish & Portuguese literature
• 870 - Italic literature; Latin
• 880 - Hellenic literature; Classical Greek
• 890 - Literature of other languages

900 - Geography & history

• 910 - Geography & travel
• 920 - Group Biography
• 921 Individual Biography
• 930 - History of the ancient world
• 940 - General history of Europe
• 950 - General history of Asia; Far East
• 960 - General history of Africa
• 970 - General history of North America
• 979.8 History of Alaska
• 980 - General history of South America
• 990 - General history of other areas

1. How to organize and operate a small library / by Genore H. Bernhard. Fort Atkinson, Wis. : Highsmith Co., c1975.