Classification System

The Library of Congress Classification System

(a) Each major subject is designated a letter from the English alphabet excluding

“I” and “O” e.g. Science general is a major subject area and is classified as “Q”.

(b) Specific subjects within each major subject area are classified by using a

combination of two letters to indicate that it is a subdivision of the major subject

e.g. Mathematics is a subject within science and it is classified under “QA”.

Physics is a subject within science and is classified under “QC”.

(c) Topics under specific subjects are classified by addition of Arabic numbers to the two letters, for example

1.Calculus-a topic in mathematics is classified under “QA303.2”.

  1. Statistical physics–a topic in physics is classified under “QC 21.2”

In summary the Library of Congress Classification Scheme consists of the following components:

Subject area Major class Sub-class Class No. Call No.
Broad subject Specific subject Specific topic
Science Q
Mathematics QA
Calculus QA303.2 QA303.2.L38

The above subject is taken as an example of the major class, sub class and class numbers within the Library of Congress Classification Scheme. See the outline below of all subjects.


A – General Works PS – American Literature
B – Philosophy-Religion-Psychology Q – Science
C – History (Civilization) QA – Mathematics
D – History (Except America) QB – Astronomy
E – American History QC – Physics
F – Local American, Latin American History QD – Chemistry
G – Geography-Anthropology QE – Geology
H – Social Sciences QH – Biology
J – Political Science QK – Botany
K – Law QL – Zoology
L – Education QM – Human Anatomy
M – Music Scores QP – Physiology
ML – Music (Literature of Music) QR – Microbiology
N – Fine Arts R – Medicine
P – Linguistics S – Agriculture
PC – Romance Languages T – Technology
PD – Germanic Languages U – Military Science
PE – English Language V – Naval Science
PQ – Romance Literature Z – Bibliography, Library Science
PR – English Literature