How To Read Library of Congress Call Numbers

Library of Congress call numbers are used to locate books and other materials in the library. The call numbers consist of letters and numbers read from top to bottom. The first line indicates the broad subject area to which the book is related.

Starting with the letter(s) at the top left of the call number, books are arranged ALPHABETICALLY:

A AC AG AZ B BC

Books having the same letter(s) on the TOP LINE are all shelved together by the number group that follows the letter(s). These numbers are arranged NUMERICALLY:

F
1 F
21 F
75 F
101 F
175 F
200

When both the letter(s) and the number group that follows are the same, books are shelved ALPHABETICALLY by the next letter:

QM
23
.A QM
23
.B QM
23
.C QM
23
.D QM
23
.E QM
23
.F

Books, which are identical in first letter(s), in the number group that follows, and in the second letter, are shelved by the next number group. These numbers are arranged DECIMALLY:

QM
23
.E6543 QM
23
.E778 QM
23
.E88 QM
23
.E9 QM
23
.E99 QM
23
.E995

In some cases a call number will have a fourth line which contains a letter and a number or numbers. The letter in this line is arranged ALPHABETICALLY, while the number is arranged DECIMALLY:

QM
23
.E6543
A25 QM
23
.E778
C6 QM
23
.E88
F88 QM
23
.E9
F885 QM
23
.E99
F9 QM
23
.E995
H92

NOTE: The publication date of a work can sometimes be determined by its inclusion at the end of the call number. However, the most accurate way to determine the date is by consulting the information given in the preliminary pages of the book.

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