Imagine you were starting a library and you had a few thousand books, magazines and other materials. How would you organize all those sources so people could easily find things? What if your collection grew to a few million items? Could your collection logically adapt and expand?

Basically, libraries organize their collections by subject. These subjects are represented by call number systems called classification systems. There are two major classification systems that your library might use: the Dewey Decimal System with call numbers that begin with numbers, and the Library of Congress (LC) Classification System with call numbers that begin with letters.