Library of Congress Call Numbers

Understanding Library of Congress (LC) Call Numbers

Our catalog uses the Library of Congress classification system, an alphanumeric system which groups books by subject categories, or classes. Below, we explain what a call number is, how to read call numbers, the shelving and filing rules of call numbers, and LC classification.

What is a call number?

A call number is like an address; it tells you where the book is located on the shelf. Each book, CD-ROM, journal, etc., has its own unique call number which is attached to the book's spine or upper left hand corner of the cover (or envelope). A book's call number also appears in the catalog entry in the library's online catalog (OPAC).


Reading Call Numbers

The Library of Congress arranges materials by subject, or 'class' (see the last section below for more information on classes). The first section of the call number represents the subject of the book. The second section often represents the author's name, and the last section is the date of publication.

In the following example of a call number for the book "What you need to know about developing study skills" by Marcia J. Coman published in 1991. LB2395 is the subject (Methods of Study), .C65 represents the author's last name (Coman), and 1991 is the year of publication.


Shelving/Filing Rules of LC Call numbers

Single letters are filed before double letters:


The second part of a call number is made up of a number that may have one or more digits. This line is read numerically. A call number with a smaller number is shelved before one that has a larger number. Some of these numbers may be divided by a point: these are also read numerically (smaller numbers are shelved before larger numbers)


The third part is the trickiest part of the call number. This part of the call number is called the "cutter". The numbers in this part are treated like decimals.

Follow these general rules when dealing with cutter numbers:

 1. Treat the letter of the cutter number alphabetically. For example, cutter numbers beginning with .B are shelved before those starting with .E.
 2. Smaller first digits after the letter are shelved before larger ones. For example, all cutter numbers beginning with .E3 would be shelved before all cutter numbers beginning with .E4, and those would be shelved before cutters beginning with .E8.
 3. Smaller second, third, etc. digits are shelved before larger ones. For example, cutters beginning with .E35 are shelved before cutters beginning with .E39. Likewise, for the third number: .E353 is shelved before .E355 and .E359.
 4. Items with only one digit after the letter are shelved before items with multiple digits beginning with the same number(s). So, the cutter number .E3 is shelved before .E35 , which is shelved before .E359.


Sometimes there are TWO cutter numbers in a call number. The first cutter, in these cases, is related to the subject of the work. The second cutter is related to the author. The shelving order of the second cutter follows the same four rules described above.

QE787 .C59C66
QE787 .C59S27
QE862 .D5L35
QE862 .D5L457
QE862 .D5L46

Sometimes, the top of the call number has the item's location: "Ref" for Reference room, etc. The final lines of the call numbers may include copy numbers, issue numbers, volume indicators and other annotations such as supplement or index specifiers. For example, the call numbers below are shelved in Reference:

QL45 .A6
QL45 .A6
QL46 .D55
.D55 1999
1999 plates

Library of Congress Classification:

To recap, a call number is a subject formula that groups materials by subject categories, or classes. Each class is identified by a letter. Classes are broken down into subclasses by adding more letters. These subclasses, in turn, are more finely delineated by numbers. Using the scheme, books are grouped together on the shelf, making it easier for you to browse the library's holdings on a specific topic. For a detailed breakdown of the subject categories, see the Library of Congress Classification Outline .

In the AMNH Library, many of our books are classed in QL (Zoology), which is a subclass in the major class Q (Science). Here is a breakdown of class QL:

QL1-355  General zoology
QL360-599.82  Invertebrates
QL461-599.82  Insects
QL605-739.8  Chordates, Vertebrates
QL614-639.8  Fishes
QL640-669.3  Reptiles and amphibians
QL671-699  Birds
QL700-739.8  Mammals
QL750-795  Animal Behavior
QL791-795  Stories & anecdotes
QL799-799.5  Morphology
QL801-950.9  Anatomy
QL951-991  Embryology

Still Need Help? Please contact the Reference Desk (x5400 or Email) for assistance. We are happy to help!