How do I use a call number to find a book on the shelf?

Library of Congress call numbers are arranged alphabetically and numerically. Read call numbers from left to right and from top to bottom.

What do the numbers and letters in the call number actually mean?

LC call numbers begin with letters that represent subject divisions. Following the initial letters are numbers that help define the subject of the material.

This call number system allows materials on related subjects to be shelved in the same area. For example, if you go to the book shelves to locate the call number QP376 .A4225 2009, other books on Neurophysiology will be found nearby.


Letters in the first line of the call number are shelved in alphabetical order.


The second line of a call number is shelved in numerical order.

QA    QA    QA    QA
50 55 76  76.15

The third line is the trickiest part of the call number. The letter is shelved alphabetical. The numbers, however, are shelved in decimal order as if there was an invisible decimal between the letter and the number.

450 450 450 450
.K346     .K40     .K5     .L11

The final lines of the call numbers may include dates, volume indicators, and copy numbers. These annotations are read after the call number.

10 10 10 10
C3 C3 C3 C3
c. 1     1933     1990     1996


The Lives of the Brain: Human Evolution and the Organ of Mind by John S. Allen.

QP represents a specific area of science, i.e. Physiology
376 defines book as Neurophysiology
.A4225   is a code for the author's last name, i.e. Allen
2009 the year of publication

This entry has been adapted from this page by Mindy Thuna.

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