Online Catalog (OPAC): A Guide to Use: The Library of Congress Classification System

The Sawyer Library, like most academic libraries, uses the Library of Congress Classification System (LCC) to organize most of the materials held in the library. This system of classification assigns a unique alphanumeric string to items so they can be placed on a shelf and easily retrieved when needed. This alphanumeric string is called a call number and is created by isolating the subject of the material, its author, and the date of publication. This practice brings together on the shelf materials with similar subjects so users can browse the shelves and discover other useful works.

Although call numbers are used to organize many library materials, such as CDs and DVDs, most items with a call number are books. A book's call number can be found in two places: the book's spine and its catalog record:

The first letters of a call number, which represent a broad category, are followed by a number that refines that broad category into a narrower topic. For example, in the book spine to the right "PN1995.9" is the number that the Library of Congress assigns to materials that deal with special topics in motion pictures: PN is for "Literature" (which includes dramas, such as broadcast media and motion pictures) and 1995.9 is for "Other special topics". ".H6" is then added to indicate that the special topic is "Horror films". Therefore PN1995.9 .H6 translates to "Horror films". Since there are many books written about horror films, further refinement is necessary to differentiate unique materials. To do this, the Library of Congress adds "C5" to represent the author's name. To make a number even more unique, the publication date is added after the author's name.

The LCC system is broken down into 21 broad categories, called classification schedules, and each is divided into smaller subjects. For example, schedule B broadly categorizes Philosophy, Psychology, and Religion, which is further refined into smaller subjects: Logic is classed under BC, Psychology under BF, Ethics under BJ, Judaism under BM, Islam under BP, and Christianity under BR. Below is a general outline of the schedules; to see a more detailed outline of the subclasses, visit the Classification Outline at the Library of Congress.

You may be wondering why some classes are missing. Classes I & O are not used, and probably will not be used in the future, because letters I & O can easily be confused with numbers 1 & 0. W, X, Y are either used for other systems or are being saved for future expansion of the LCC system.