The books in the University of Chicago Library generally are arranged on the shelves according to the Library of Congress Classification Scheme , which separates all knowledge into 21 classes. Each subject class is identified by a letter of the alphabet, with subclasses defined by additional letters, and subtopics within classes and subclasses by additional numerical notation. The call number JK216.T7 1966a v.1 c.2, representing an edition of Democracy in America by Alexis de Tocqueville, illustrates these and other parts of this call number:

J K 2 1 6 = Classification number:

J = General Subject (Political Science)
K = Specific Subject (United States)
261 = Aspect of the subject (Constitutional History, 1821-1865)

Numbers after the decimal point file as decimal numbers.

.T7 1966a v.1 c.2 = Book number:

.T7 = Tocqueville (derived commonly from author's name or the title)
1966 = Year of publication of this edition
a = Letter indicates that this is the 2nd 1966 edition in the Library
v.1 = Volume number (in multivolume sets or serials)
c.2 = Copy number (used to distinguish one library copy from another)

Note: No two physical pieces will ever have exactly the same call number.

Books are arranged on the shelves sequentially by classification number. For example, in the D section (History) the basic call number arrangement is as follows: D, DA, DB, DC, . . . DZ; E; F; (etc.)

Within each letter group, the sub-arrangement is numerical. For example:

D1, D2, . . . D11; . . . D16.5; . . . D110; . . . D9999; DA1, . . . (etc.)

Within each classification number the sub-arrangement is again alphabetical. For example:

D1.A1, D1.B1, D1.C1, . . . D1.Z1; . . . D2.A1 . . . (etc.)

Within each book number the sub-arrangement is by decimal number. For example:

D1.A1, . . . D1.A101, . . . D1.A11, . . . D1.A199, . . . D1.A2, (etc.)