The Library of Congress Classification System (LCCS) was developed in the late 19th and early 20th century to organize the book collections of the Library of Congress. Over time, the LC system has been adopted by many libraries, especially big Academic Libraries around the world. The LCCS divides all knowledge into 21 basic classes identified by a single letter of the alphabets.

The Dewey Decimal Classification (DDC) system was developed by Melvil Dewey in 1876. The DDC divided all knowledge into 10 basic classes identified by numbers. Below is a list that maps the LC headings to DDC.

                LCCS                                                       DDC

A	General Works	000	Generalities
B	Philosophy, Psychology, Religion	100 and 200	Philosophy, Religion &   Psychology
C	History of Ancient World, History of Civilization	930 and 974-998	History of Ancient World (to circa 499 AD), General History
D	World History and History of Europe, Asia, Africa, Australia, New Zealand	909	World History
E	History of the Americas	970-979	History of North America
F	History of the Americas	980-989	History of South America
G	Geography, Anthropology, Recreation	900	Geography and History
H	Social Sciences	300	Social Sciences
J	Political Science	379	Government Regulation, Control, Support
K	Law	340-349	Law
L	Education	370-378	Education
M	Music and Books on Music	780-788	Music
N	Fine Arts	700	The Arts
P	Language and Literature	400 and 800	Language and Literature & Rhetoric
Q	Science	500	Natural Sciences & Mathematics
R	Medicine	610-619	Technology (Applied Sciences)
S	Agriculture	630-639	Agriculture
T	Technology	620-629	Engineering
U	Military Science	355	Military Science
V	Naval Science	359	Sea (Naval) Forces and Warfare
Z	Bibliography, Library Science, Information Resources (General)	020-028	Library & Information Sciences

Sources: "Library of Congress Classification Outline". The Library of Congress. n.d. Web. 3 Jul. 2012. (http://www.loc.gov/catdir/cpso/lcco/)
"Dewey Decimal System: A Guide to Call Numbers". University Library, University of Illinois at Urbana Champaign. 6 Jun. 2011. Web. 3 Jul. 2012. (http://www.library.illinois.edu/ugl/about/dewey.html).